Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney:

- Documentation updates.

- Miscellaneous fixes.

- Preemptible-RCU fixes, including fixing an old bug in the
interaction of RCU priority boosting and CPU hotplug.

- SRCU updates.

- RCU CPU stall-warning updates.

- RCU torture-test updates.

Signed-off-by: Ingo Molnar <[e-mail]>

Documentation/RCU/stallwarn.txt

···
 	21 seconds.
 
 	This configuration parameter may be changed at runtime via the
-	/sys/module/rcutree/parameters/rcu_cpu_stall_timeout, however
+	/sys/module/rcupdate/parameters/rcu_cpu_stall_timeout, however
 	this parameter is checked only at the beginning of a cycle.
 	So if you are 10 seconds into a 40-second stall, setting this
 	sysfs parameter to (say) five will shorten the timeout for the
···
 "D" indicates that dyntick-idle processing is enabled ("." is printed
 otherwise, for example, if disabled via the "nohz=" kernel boot parameter).
 
+If the relevant grace-period kthread has been unable to run prior to
+the stall warning, the following additional line is printed:
+
+	rcu_preempt kthread starved for 2023 jiffies!
+
+Starving the grace-period kthreads of CPU time can of course result in
+RCU CPU stall warnings even when all CPUs and tasks have passed through
+the required quiescent states.
+
 
 Multiple Warnings From One Stall
 
···
 	if the looping in the kernel is really expected and desirable
 	behavior, you might need to replace some of the cond_resched()
 	calls with calls to cond_resched_rcu_qs().
+
+o	Anything that prevents RCU's grace-period kthreads from running.
+	This can result in the "All QSes seen" console-log message.
+	This message will include information on when the kthread last
+	ran and how often it should be expected to run.
 
 o	A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might
 	happen to preempt a low-priority task in the middle of an RCU

Documentation/RCU/trace.txt

···
 
 The output of "cat rcu/rcu_preempt/rcudata" looks as follows:
 
-  0!c=30455 g=30456 pq=1 qp=1 dt=126535/140000000000000/0 df=2002 of=4 ql=0/0 qs=N... b=10 ci=74572 nci=0 co=1131 ca=716
-  1!c=30719 g=30720 pq=1 qp=0 dt=132007/140000000000000/0 df=1874 of=10 ql=0/0 qs=N... b=10 ci=123209 nci=0 co=685 ca=982
-  2!c=30150 g=30151 pq=1 qp=1 dt=138537/140000000000000/0 df=1707 of=8 ql=0/0 qs=N... b=10 ci=80132 nci=0 co=1328 ca=1458
-  3 c=31249 g=31250 pq=1 qp=0 dt=107255/140000000000000/0 df=1749 of=6 ql=0/450 qs=NRW. b=10 ci=151700 nci=0 co=509 ca=622
-  4!c=29502 g=29503 pq=1 qp=1 dt=83647/140000000000000/0 df=965 of=5 ql=0/0 qs=N... b=10 ci=65643 nci=0 co=1373 ca=1521
-  5 c=31201 g=31202 pq=1 qp=1 dt=70422/0/0 df=535 of=7 ql=0/0 qs=.... b=10 ci=58500 nci=0 co=764 ca=698
-  6!c=30253 g=30254 pq=1 qp=1 dt=95363/140000000000000/0 df=780 of=5 ql=0/0 qs=N... b=10 ci=100607 nci=0 co=1414 ca=1353
-  7 c=31178 g=31178 pq=1 qp=0 dt=91536/0/0 df=547 of=4 ql=0/0 qs=.... b=10 ci=109819 nci=0 co=1115 ca=969
+  0!c=30455 g=30456 pq=1/0 qp=1 dt=126535/140000000000000/0 df=2002 of=4 ql=0/0 qs=N... b=10 ci=74572 nci=0 co=1131 ca=716
+  1!c=30719 g=30720 pq=1/0 qp=0 dt=132007/140000000000000/0 df=1874 of=10 ql=0/0 qs=N... b=10 ci=123209 nci=0 co=685 ca=982
+  2!c=30150 g=30151 pq=1/1 qp=1 dt=138537/140000000000000/0 df=1707 of=8 ql=0/0 qs=N... b=10 ci=80132 nci=0 co=1328 ca=1458
+  3 c=31249 g=31250 pq=1/1 qp=0 dt=107255/140000000000000/0 df=1749 of=6 ql=0/450 qs=NRW. b=10 ci=151700 nci=0 co=509 ca=622
+  4!c=29502 g=29503 pq=1/0 qp=1 dt=83647/140000000000000/0 df=965 of=5 ql=0/0 qs=N... b=10 ci=65643 nci=0 co=1373 ca=1521
+  5 c=31201 g=31202 pq=1/0 qp=1 dt=70422/0/0 df=535 of=7 ql=0/0 qs=.... b=10 ci=58500 nci=0 co=764 ca=698
+  6!c=30253 g=30254 pq=1/0 qp=1 dt=95363/140000000000000/0 df=780 of=5 ql=0/0 qs=N... b=10 ci=100607 nci=0 co=1414 ca=1353
+  7 c=31178 g=31178 pq=1/0 qp=0 dt=91536/0/0 df=547 of=4 ql=0/0 qs=.... b=10 ci=109819 nci=0 co=1115 ca=969
 
 This file has one line per CPU, or eight for this 8-CPU system.
 The fields are as follows:
···
 Kernels compiled with CONFIG_RCU_BOOST=y display the following from
 /debug/rcu/rcu_preempt/rcudata:
 
-  0!c=12865 g=12866 pq=1 qp=1 dt=83113/140000000000000/0 df=288 of=11 ql=0/0 qs=N... kt=0/O ktl=944 b=10 ci=60709 nci=0 co=748 ca=871
-  1 c=14407 g=14408 pq=1 qp=0 dt=100679/140000000000000/0 df=378 of=7 ql=0/119 qs=NRW. kt=0/W ktl=9b6 b=10 ci=109740 nci=0 co=589 ca=485
-  2 c=14407 g=14408 pq=1 qp=0 dt=105486/0/0 df=90 of=9 ql=0/89 qs=NRW. kt=0/W ktl=c0c b=10 ci=83113 nci=0 co=533 ca=490
-  3 c=14407 g=14408 pq=1 qp=0 dt=107138/0/0 df=142 of=8 ql=0/188 qs=NRW. kt=0/W ktl=b96 b=10 ci=121114 nci=0 co=426 ca=290
-  4 c=14405 g=14406 pq=1 qp=1 dt=50238/0/0 df=706 of=7 ql=0/0 qs=.... kt=0/W ktl=812 b=10 ci=34929 nci=0 co=643 ca=114
-  5!c=14168 g=14169 pq=1 qp=0 dt=45465/140000000000000/0 df=161 of=11 ql=0/0 qs=N... kt=0/O ktl=b4d b=10 ci=47712 nci=0 co=677 ca=722
-  6 c=14404 g=14405 pq=1 qp=0 dt=59454/0/0 df=94 of=6 ql=0/0 qs=.... kt=0/W ktl=e57 b=10 ci=55597 nci=0 co=701 ca=811
-  7 c=14407 g=14408 pq=1 qp=1 dt=68850/0/0 df=31 of=8 ql=0/0 qs=.... kt=0/W ktl=14bd b=10 ci=77475 nci=0 co=508 ca=1042
+  0!c=12865 g=12866 pq=1/0 qp=1 dt=83113/140000000000000/0 df=288 of=11 ql=0/0 qs=N... kt=0/O ktl=944 b=10 ci=60709 nci=0 co=748 ca=871
+  1 c=14407 g=14408 pq=1/0 qp=0 dt=100679/140000000000000/0 df=378 of=7 ql=0/119 qs=NRW. kt=0/W ktl=9b6 b=10 ci=109740 nci=0 co=589 ca=485
+  2 c=14407 g=14408 pq=1/0 qp=0 dt=105486/0/0 df=90 of=9 ql=0/89 qs=NRW. kt=0/W ktl=c0c b=10 ci=83113 nci=0 co=533 ca=490
+  3 c=14407 g=14408 pq=1/0 qp=0 dt=107138/0/0 df=142 of=8 ql=0/188 qs=NRW. kt=0/W ktl=b96 b=10 ci=121114 nci=0 co=426 ca=290
+  4 c=14405 g=14406 pq=1/0 qp=1 dt=50238/0/0 df=706 of=7 ql=0/0 qs=.... kt=0/W ktl=812 b=10 ci=34929 nci=0 co=643 ca=114
+  5!c=14168 g=14169 pq=1/0 qp=0 dt=45465/140000000000000/0 df=161 of=11 ql=0/0 qs=N... kt=0/O ktl=b4d b=10 ci=47712 nci=0 co=677 ca=722
+  6 c=14404 g=14405 pq=1/0 qp=0 dt=59454/0/0 df=94 of=6 ql=0/0 qs=.... kt=0/W ktl=e57 b=10 ci=55597 nci=0 co=701 ca=811
+  7 c=14407 g=14408 pq=1/0 qp=1 dt=68850/0/0 df=31 of=8 ql=0/0 qs=.... kt=0/W ktl=14bd b=10 ci=77475 nci=0 co=508 ca=1042
 
 This is similar to the output discussed above, but contains the following
 additional fields:

Documentation/memory-barriers.txt

···
 	STORE *(A + 4) = Y; STORE *A = X;
 	STORE {*A, *(A + 4) } = {X, Y};
 
+And there are anti-guarantees:
+
+ (*) These guarantees do not apply to bitfields, because compilers often
+     generate code to modify these using non-atomic read-modify-write
+     sequences.  Do not attempt to use bitfields to synchronize parallel
+     algorithms.
+
+ (*) Even in cases where bitfields are protected by locks, all fields
+     in a given bitfield must be protected by one lock.  If two fields
+     in a given bitfield are protected by different locks, the compiler's
+     non-atomic read-modify-write sequences can cause an update to one
+     field to corrupt the value of an adjacent field.
+
+ (*) These guarantees apply only to properly aligned and sized scalar
+     variables.  "Properly sized" currently means variables that are
+     the same size as "char", "short", "int" and "long".  "Properly
+     aligned" means the natural alignment, thus no constraints for
+     "char", two-byte alignment for "short", four-byte alignment for
+     "int", and either four-byte or eight-byte alignment for "long",
+     on 32-bit and 64-bit systems, respectively.  Note that these
+     guarantees were introduced into the C11 standard, so beware when
+     using older pre-C11 compilers (for example, gcc 4.6).  The portion
+     of the standard containing this guarantee is Section 3.14, which
+     defines "memory location" as follows:
+
+     	memory location
+		either an object of scalar type, or a maximal sequence
+		of adjacent bit-fields all having nonzero width
+
+		NOTE 1: Two threads of execution can update and access
+		separate memory locations without interfering with
+		each other.
+
+		NOTE 2: A bit-field and an adjacent non-bit-field member
+		are in separate memory locations. The same applies
+		to two bit-fields, if one is declared inside a nested
+		structure declaration and the other is not, or if the two
+		are separated by a zero-length bit-field declaration,
+		or if they are separated by a non-bit-field member
+		declaration. It is not safe to concurrently update two
+		bit-fields in the same structure if all members declared
+		between them are also bit-fields, no matter what the
+		sizes of those intervening bit-fields happen to be.
+
 
 =========================
 WHAT ARE MEMORY BARRIERS?
···
       However, they do -not- guarantee any other sort of ordering:
       Not prior loads against later loads, nor prior stores against
       later anything.  If you need these other forms of ordering,
-      use smb_rmb(), smp_wmb(), or, in the case of prior stores and
+      use smp_rmb(), smp_wmb(), or, in the case of prior stores and
       later loads, smp_mb().
 
   (*) If both legs of the "if" statement begin with identical stores

arch/arm/kvm/Kconfig

···
 	select HAVE_KVM_CPU_RELAX_INTERCEPT
 	select KVM_MMIO
 	select KVM_ARM_HOST
+	select SRCU
 	depends on ARM_VIRT_EXT && ARM_LPAE
 	---help---
 	  Support hosting virtualized guest machines. You will also

arch/arm64/kvm/Kconfig

···
 	select KVM_ARM_HOST
 	select KVM_ARM_VGIC
 	select KVM_ARM_TIMER
+	select SRCU
 	---help---
 	  Support hosting virtualized guest machines.
 

arch/mips/kvm/Kconfig

···
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES
 	select KVM_MMIO
+	select SRCU
 	---help---
 	  Support for hosting Guest kernels.
 	  Currently supported on MIPS32 processors.

arch/powerpc/kvm/Kconfig

···
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES
 	select HAVE_KVM_EVENTFD
+	select SRCU
 
 config KVM_BOOK3S_HANDLER
 	bool

arch/s390/kvm/Kconfig

···
 	select HAVE_KVM_IRQCHIP
 	select HAVE_KVM_IRQFD
 	select HAVE_KVM_IRQ_ROUTING
+	select SRCU
 	---help---
 	  Support hosting paravirtualized guest machines using the SIE
 	  virtualization capability on the mainframe. This should work

arch/tile/kvm/Kconfig

···
 	depends on HAVE_KVM && MODULES
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES
+	select SRCU
 	---help---
 	  Support hosting paravirtualized guest machines.
 

arch/x86/Kconfig

···
 	select HAVE_ACPI_APEI_NMI if ACPI
 	select ACPI_LEGACY_TABLES_LOOKUP if ACPI
 	select X86_FEATURE_NAMES if PROC_FS
+	select SRCU
 
 config INSTRUCTION_DECODER
 	def_bool y

arch/x86/kvm/Kconfig

···
 	select HAVE_KVM_MSI
 	select HAVE_KVM_CPU_RELAX_INTERCEPT
 	select KVM_VFIO
+	select SRCU
 	---help---
 	  Support hosting fully virtualized guest machines using hardware
 	  virtualization extensions.  You will need a fairly recent

drivers/clk/Kconfig

···
 	bool
 	select HAVE_CLK_PREPARE
 	select CLKDEV_LOOKUP
+	select SRCU
 	---help---
 	  The common clock framework is a single definition of struct
 	  clk, useful across many platforms, as well as an

drivers/cpufreq/Kconfig

···
 
 config CPU_FREQ
 	bool "CPU Frequency scaling"
+	select SRCU
 	help
 	  CPU Frequency scaling allows you to change the clock speed of 
 	  CPUs on the fly. This is a nice method to save power, because 

drivers/devfreq/Kconfig

···
 menuconfig PM_DEVFREQ
 	bool "Generic Dynamic Voltage and Frequency Scaling (DVFS) support"
+	select SRCU
 	help
 	  A device may have a list of frequencies and voltages available.
 	  devfreq, a generic DVFS framework can be registered for a device

drivers/md/Kconfig

···
 menuconfig MD
 	bool "Multiple devices driver support (RAID and LVM)"
 	depends on BLOCK
+	select SRCU
 	help
 	  Support multiple physical spindles through a single logical device.
 	  Required for RAID and logical volume management.

drivers/net/Kconfig

···
 
 config NETPOLL
 	def_bool NETCONSOLE
+	select SRCU
 
 config NET_POLL_CONTROLLER
 	def_bool NETPOLL

fs/btrfs/Kconfig

···
 	select LZO_DECOMPRESS
 	select RAID6_PQ
 	select XOR_BLOCKS
+	select SRCU
 
 	help
 	  Btrfs is a general purpose copy-on-write filesystem with extents,

fs/notify/Kconfig

···
 config FSNOTIFY
 	def_bool n
+	select SRCU
 
 source "fs/notify/dnotify/Kconfig"
 source "fs/notify/inotify/Kconfig"

fs/quota/Kconfig

···
 config QUOTA
 	bool "Quota support"
 	select QUOTACTL
+	select SRCU
 	help
 	  If you say Y here, you will be able to set per user limits for disk
 	  usage (also called disk quotas). Currently, it works for the

include/linux/compiler.h

···
 
 /* Is this type a native word size -- useful for atomic operations */
 #ifndef __native_word
-# define __native_word(t) (sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
+# define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
 #endif
 
 /* Compile time object size, -1 for unknown */

include/linux/rculist.h

···
  * @member:	the name of the hlist_node within the struct.
  */
 #define hlist_for_each_entry_continue_rcu(pos, member)			\
-	for (pos = hlist_entry_safe(rcu_dereference((pos)->member.next),\
-			typeof(*(pos)), member);			\
+	for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
+			&(pos)->member)), typeof(*(pos)), member);	\
 	     pos;							\
-	     pos = hlist_entry_safe(rcu_dereference((pos)->member.next),\
-			typeof(*(pos)), member))
+	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(	\
+			&(pos)->member)), typeof(*(pos)), member))
 
 /**
  * hlist_for_each_entry_continue_rcu_bh - iterate over a hlist continuing after current point
···
  * @member:	the name of the hlist_node within the struct.
  */
 #define hlist_for_each_entry_continue_rcu_bh(pos, member)		\
-	for (pos = hlist_entry_safe(rcu_dereference_bh((pos)->member.next),\
-			typeof(*(pos)), member);			\
+	for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(  \
+			&(pos)->member)), typeof(*(pos)), member);	\
 	     pos;							\
-	     pos = hlist_entry_safe(rcu_dereference_bh((pos)->member.next),\
-			typeof(*(pos)), member))
+	     pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(	\
+			&(pos)->member)), typeof(*(pos)), member))
 
 /**
  * hlist_for_each_entry_from_rcu - iterate over a hlist continuing from current point

include/linux/rcupdate.h

···
 extern struct srcu_struct tasks_rcu_exit_srcu;
 #define rcu_note_voluntary_context_switch(t) \
 	do { \
+		rcu_all_qs(); \
 		if (ACCESS_ONCE((t)->rcu_tasks_holdout)) \
 			ACCESS_ONCE((t)->rcu_tasks_holdout) = false; \
 	} while (0)
 #else /* #ifdef CONFIG_TASKS_RCU */
 #define TASKS_RCU(x) do { } while (0)
-#define rcu_note_voluntary_context_switch(t)	do { } while (0)
+#define rcu_note_voluntary_context_switch(t)	rcu_all_qs()
 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 
 /**
···
 })
 #define __rcu_dereference_check(p, c, space) \
 ({ \
-	typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
+	/* Dependency order vs. p above. */ \
+	typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
 	rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \
 	rcu_dereference_sparse(p, space); \
-	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
-	((typeof(*p) __force __kernel *)(_________p1)); \
+	((typeof(*p) __force __kernel *)(________p1)); \
 })
 #define __rcu_dereference_protected(p, c, space) \
 ({ \
···
 })
 #define __rcu_dereference_index_check(p, c) \
 ({ \
-	typeof(p) _________p1 = ACCESS_ONCE(p); \
+	/* Dependency order vs. p above. */ \
+	typeof(p) _________p1 = lockless_dereference(p); \
 	rcu_lockdep_assert(c, \
 			   "suspicious rcu_dereference_index_check() usage"); \
-	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
 	(_________p1); \
 })
 

include/linux/rcutiny.h

···
 }
 
 /*
- * Return the number of grace periods.
+ * Return the number of grace periods started.
  */
-static inline long rcu_batches_completed(void)
+static inline unsigned long rcu_batches_started(void)
 {
 	return 0;
 }
 
 /*
- * Return the number of bottom-half grace periods.
+ * Return the number of bottom-half grace periods started.
  */
-static inline long rcu_batches_completed_bh(void)
+static inline unsigned long rcu_batches_started_bh(void)
+{
+	return 0;
+}
+
+/*
+ * Return the number of sched grace periods started.
+ */
+static inline unsigned long rcu_batches_started_sched(void)
+{
+	return 0;
+}
+
+/*
+ * Return the number of grace periods completed.
+ */
+static inline unsigned long rcu_batches_completed(void)
+{
+	return 0;
+}
+
+/*
+ * Return the number of bottom-half grace periods completed.
+ */
+static inline unsigned long rcu_batches_completed_bh(void)
+{
+	return 0;
+}
+
+/*
+ * Return the number of sched grace periods completed.
+ */
+static inline unsigned long rcu_batches_completed_sched(void)
 {
 	return 0;
 }
···
 	return true;
 }
 
-
 #endif /* #else defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
+
+static inline void rcu_all_qs(void)
+{
+}
 
 #endif /* __LINUX_RCUTINY_H */

include/linux/rcutree.h

···
 
 extern unsigned long rcutorture_testseq;
 extern unsigned long rcutorture_vernum;
-long rcu_batches_completed(void);
-long rcu_batches_completed_bh(void);
-long rcu_batches_completed_sched(void);
+unsigned long rcu_batches_started(void);
+unsigned long rcu_batches_started_bh(void);
+unsigned long rcu_batches_started_sched(void);
+unsigned long rcu_batches_completed(void);
+unsigned long rcu_batches_completed_bh(void);
+unsigned long rcu_batches_completed_sched(void);
 void show_rcu_gp_kthreads(void);
 
 void rcu_force_quiescent_state(void);
···
 extern int rcu_scheduler_active __read_mostly;
 
 bool rcu_is_watching(void);
+
+void rcu_all_qs(void);
 
 #endif /* __LINUX_RCUTREE_H */

include/linux/srcu.h

···
 #define RCU_BATCH_INIT(name) { NULL, &(name.head) }
 
 struct srcu_struct {
-	unsigned completed;
+	unsigned long completed;
 	struct srcu_struct_array __percpu *per_cpu_ref;
 	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
 	bool running;
···
  * define and init a srcu struct at build time.
  * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it.
  */
-#define DEFINE_SRCU(name)						\
+#define __DEFINE_SRCU(name, is_static)					\
 	static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
-	struct srcu_struct name = __SRCU_STRUCT_INIT(name);
-
-#define DEFINE_STATIC_SRCU(name)					\
-	static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
-	static struct srcu_struct name = __SRCU_STRUCT_INIT(name);
+	is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+#define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
+#define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
 
 /**
  * call_srcu() - Queue a callback for invocation after an SRCU grace period
···
 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 void synchronize_srcu(struct srcu_struct *sp);
 void synchronize_srcu_expedited(struct srcu_struct *sp);
-long srcu_batches_completed(struct srcu_struct *sp);
+unsigned long srcu_batches_completed(struct srcu_struct *sp);
 void srcu_barrier(struct srcu_struct *sp);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC

init/Kconfig

···
 config TREE_RCU
 	bool "Tree-based hierarchical RCU"
 	depends on !PREEMPT && SMP
-	select IRQ_WORK
 	help
 	  This option selects the RCU implementation that is
 	  designed for very large SMP system with hundreds or
···
 config PREEMPT_RCU
 	bool "Preemptible tree-based hierarchical RCU"
 	depends on PREEMPT
-	select IRQ_WORK
 	help
 	  This option selects the RCU implementation that is
 	  designed for very large SMP systems with hundreds or
···
 
 endchoice
 
+config SRCU
+	bool
+	help
+	  This option selects the sleepable version of RCU. This version
+	  permits arbitrary sleeping or blocking within RCU read-side critical
+	  sections.
+
 config TASKS_RCU
 	bool "Task_based RCU implementation using voluntary context switch"
 	default n
+	select SRCU
 	help
 	  This option enables a task-based RCU implementation that uses
 	  only voluntary context switch (not preemption!), idle, and
···
 
 config RCU_KTHREAD_PRIO
 	int "Real-time priority to use for RCU worker threads"
-	range 1 99
-	depends on RCU_BOOST
-	default 1
+	range 1 99 if RCU_BOOST
+	range 0 99 if !RCU_BOOST
+	default 1 if RCU_BOOST
+	default 0 if !RCU_BOOST
 	help
 	  This option specifies the SCHED_FIFO priority value that will be
 	  assigned to the rcuc/n and rcub/n threads and is also the value
···
 	depends on HAVE_PERF_EVENTS
 	select ANON_INODES
 	select IRQ_WORK
+	select SRCU
 	help
 	  Enable kernel support for various performance events provided
 	  by software and hardware.

kernel/cpu.c

···
 
 static struct {
 	struct task_struct *active_writer;
-	struct mutex lock; /* Synchronizes accesses to refcount, */
+	/* wait queue to wake up the active_writer */
+	wait_queue_head_t wq;
+	/* verifies that no writer will get active while readers are active */
+	struct mutex lock;
 	/*
 	 * Also blocks the new readers during
 	 * an ongoing cpu hotplug operation.
 	 */
-	int refcount;
-	/* And allows lockless put_online_cpus(). */
-	atomic_t puts_pending;
+	atomic_t refcount;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
 #endif
 } cpu_hotplug = {
 	.active_writer = NULL,
+	.wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq),
 	.lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
-	.refcount = 0,
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	.dep_map = {.name = "cpu_hotplug.lock" },
 #endif
···
 #define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)
 #define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)
 
-static void apply_puts_pending(int max)
-{
-	int delta;
-
-	if (atomic_read(&cpu_hotplug.puts_pending) >= max) {
-		delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
-		cpu_hotplug.refcount -= delta;
-	}
-}
 
 void get_online_cpus(void)
 {
···
 		return;
 	cpuhp_lock_acquire_read();
 	mutex_lock(&cpu_hotplug.lock);
-	apply_puts_pending(65536);
-	cpu_hotplug.refcount++;
+	atomic_inc(&cpu_hotplug.refcount);
 	mutex_unlock(&cpu_hotplug.lock);
 }
 EXPORT_SYMBOL_GPL(get_online_cpus);
···
 	if (!mutex_trylock(&cpu_hotplug.lock))
 		return false;
 	cpuhp_lock_acquire_tryread();
-	apply_puts_pending(65536);
-	cpu_hotplug.refcount++;
+	atomic_inc(&cpu_hotplug.refcount);
 	mutex_unlock(&cpu_hotplug.lock);
 	return true;
 }
···
 
 void put_online_cpus(void)
 {
+	int refcount;
+
 	if (cpu_hotplug.active_writer == current)
 		return;
-	if (!mutex_trylock(&cpu_hotplug.lock)) {
-		atomic_inc(&cpu_hotplug.puts_pending);
-		cpuhp_lock_release();
-		return;
-	}
 
-	if (WARN_ON(!cpu_hotplug.refcount))
-		cpu_hotplug.refcount++; /* try to fix things up */
+	refcount = atomic_dec_return(&cpu_hotplug.refcount);
+	if (WARN_ON(refcount < 0)) /* try to fix things up */
+		atomic_inc(&cpu_hotplug.refcount);
 
-	if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
-		wake_up_process(cpu_hotplug.active_writer);
-	mutex_unlock(&cpu_hotplug.lock);
+	if (refcount <= 0 && waitqueue_active(&cpu_hotplug.wq))
+		wake_up(&cpu_hotplug.wq);
+
 	cpuhp_lock_release();
 
 }
···
  */
 void cpu_hotplug_begin(void)
 {
-	cpu_hotplug.active_writer = current;
+	DEFINE_WAIT(wait);
 
+	cpu_hotplug.active_writer = current;
 	cpuhp_lock_acquire();
+
 	for (;;) {
 		mutex_lock(&cpu_hotplug.lock);
-		apply_puts_pending(1);
-		if (likely(!cpu_hotplug.refcount))
-			break;
-		__set_current_state(TASK_UNINTERRUPTIBLE);
+		prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE);
+		if (likely(!atomic_read(&cpu_hotplug.refcount)))
+				break;
 		mutex_unlock(&cpu_hotplug.lock);
 		schedule();
 	}
+	finish_wait(&cpu_hotplug.wq, &wait);
 }
 
 void cpu_hotplug_done(void)

kernel/notifier.c

···
 }
 EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
 
+#ifdef CONFIG_SRCU
 /*
  *	SRCU notifier chain routines.    Registration and unregistration
  *	use a mutex, and call_chain is synchronized by SRCU (no locks).
···
 	nh->head = NULL;
 }
 EXPORT_SYMBOL_GPL(srcu_init_notifier_head);
+
+#endif /* CONFIG_SRCU */
 
 static ATOMIC_NOTIFIER_HEAD(die_chain);
 

kernel/power/Kconfig

···
 
 config PM_OPP
 	bool
+	select SRCU
 	---help---
 	  SOCs have a standard set of tuples consisting of frequency and
 	  voltage pairs that the device will support per voltage domain. This

kernel/rcu/Makefile

···
-obj-y += update.o srcu.o
+obj-y += update.o
+obj-$(CONFIG_SRCU) += srcu.o
 obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_TREE_RCU) += tree.o
 obj-$(CONFIG_PREEMPT_RCU) += tree.o

kernel/rcu/rcu.h

···
 
 void rcu_early_boot_tests(void);
 
+/*
+ * This function really isn't for public consumption, but RCU is special in
+ * that context switches can allow the state machine to make progress.
+ */
+extern void resched_cpu(int cpu);
+
 #endif /* __LINUX_RCU_H */

kernel/rcu/rcutorture.c

···
 	int (*readlock)(void);
 	void (*read_delay)(struct torture_random_state *rrsp);
 	void (*readunlock)(int idx);
-	int (*completed)(void);
+	unsigned long (*started)(void);
+	unsigned long (*completed)(void);
 	void (*deferred_free)(struct rcu_torture *p);
 	void (*sync)(void);
 	void (*exp_sync)(void);
···
 static void rcu_torture_read_unlock(int idx) __releases(RCU)
 {
 	rcu_read_unlock();
-}
-
-static int rcu_torture_completed(void)
-{
-	return rcu_batches_completed();
 }
 
 /*
···
 		cur_ops->deferred_free(rp);
 }
 
-static int rcu_no_completed(void)
+static unsigned long rcu_no_completed(void)
 {
 	return 0;
 }
···
 	.readlock	= rcu_torture_read_lock,
 	.read_delay	= rcu_read_delay,
 	.readunlock	= rcu_torture_read_unlock,
-	.completed	= rcu_torture_completed,
+	.started	= rcu_batches_started,
+	.completed	= rcu_batches_completed,
 	.deferred_free	= rcu_torture_deferred_free,
 	.sync		= synchronize_rcu,
 	.exp_sync	= synchronize_rcu_expedited,
···
 	rcu_read_unlock_bh();
 }
 
-static int rcu_bh_torture_completed(void)
-{
-	return rcu_batches_completed_bh();
-}
-
 static void rcu_bh_torture_deferred_free(struct rcu_torture *p)
 {
 	call_rcu_bh(&p->rtort_rcu, rcu_torture_cb);
···
 	.readlock	= rcu_bh_torture_read_lock,
 	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
 	.readunlock	= rcu_bh_torture_read_unlock,
-	.completed	= rcu_bh_torture_completed,
+	.started	= rcu_batches_started_bh,
+	.completed	= rcu_batches_completed_bh,
 	.deferred_free	= rcu_bh_torture_deferred_free,
 	.sync		= synchronize_rcu_bh,
 	.exp_sync	= synchronize_rcu_bh_expedited,
···
 	.readlock	= rcu_torture_read_lock,
 	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
 	.readunlock	= rcu_torture_read_unlock,
+	.started	= rcu_no_completed,
 	.completed	= rcu_no_completed,
 	.deferred_free	= rcu_busted_torture_deferred_free,
 	.sync		= synchronize_rcu_busted,
···
 	srcu_read_unlock(&srcu_ctl, idx);
 }
 
-static int srcu_torture_completed(void)
+static unsigned long srcu_torture_completed(void)
 {
 	return srcu_batches_completed(&srcu_ctl);
 }
···
 	.readlock	= srcu_torture_read_lock,
 	.read_delay	= srcu_read_delay,
 	.readunlock	= srcu_torture_read_unlock,
+	.started	= NULL,
 	.completed	= srcu_torture_completed,
 	.deferred_free	= srcu_torture_deferred_free,
 	.sync		= srcu_torture_synchronize,
···
 	.readlock	= sched_torture_read_lock,
 	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
 	.readunlock	= sched_torture_read_unlock,
-	.completed	= rcu_no_completed,
+	.started	= rcu_batches_started_sched,
+	.completed	= rcu_batches_completed_sched,
 	.deferred_free	= rcu_sched_torture_deferred_free,
 	.sync		= synchronize_sched,
 	.exp_sync	= synchronize_sched_expedited,
···
 	.readlock	= tasks_torture_read_lock,
 	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
 	.readunlock	= tasks_torture_read_unlock,
+	.started	= rcu_no_completed,
 	.completed	= rcu_no_completed,
 	.deferred_free	= rcu_tasks_torture_deferred_free,
 	.sync		= synchronize_rcu_tasks,
···
 static void rcu_torture_timer(unsigned long unused)
 {
 	int idx;
-	int completed;
-	int completed_end;
+	unsigned long started;
+	unsigned long completed;
 	static DEFINE_TORTURE_RANDOM(rand);
 	static DEFINE_SPINLOCK(rand_lock);
 	struct rcu_torture *p;
···
 	unsigned long long ts;
 
 	idx = cur_ops->readlock();
-	completed = cur_ops->completed();
+	if (cur_ops->started)
+		started = cur_ops->started();
+	else
+		started = cur_ops->completed();
 	ts = rcu_trace_clock_local();
 	p = rcu_dereference_check(rcu_torture_current,
 				  rcu_read_lock_bh_held() ||
···
 		/* Should not happen, but... */
 		pipe_count = RCU_TORTURE_PIPE_LEN;
 	}
-	completed_end = cur_ops->completed();
+	completed = cur_ops->completed();
 	if (pipe_count > 1) {
 		do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu, ts,
-					  completed, completed_end);
+					  started, completed);
 		rcutorture_trace_dump();
 	}
 	__this_cpu_inc(rcu_torture_count[pipe_count]);
-	completed = completed_end - completed;
+	completed = completed - started;
+	if (cur_ops->started)
+		completed++;
 	if (completed > RCU_TORTURE_PIPE_LEN) {
 		/* Should not happen, but... */
 		completed = RCU_TORTURE_PIPE_LEN;
···
 static int
 rcu_torture_reader(void *arg)
 {
-	int completed;
-	int completed_end;
+	unsigned long started;
+	unsigned long completed;
 	int idx;
 	DEFINE_TORTURE_RANDOM(rand);
 	struct rcu_torture *p;
···
 				mod_timer(&t, jiffies + 1);
 		}
 		idx = cur_ops->readlock();
-		completed = cur_ops->completed();
+		if (cur_ops->started)
+			started = cur_ops->started();
+		else
+			started = cur_ops->completed();
 		ts = rcu_trace_clock_local();
 		p = rcu_dereference_check(rcu_torture_current,
 					  rcu_read_lock_bh_held() ||
···
 			/* Should not happen, but... */
 			pipe_count = RCU_TORTURE_PIPE_LEN;
 		}
-		completed_end = cur_ops->completed();
+		completed = cur_ops->completed();
 		if (pipe_count > 1) {
 			do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu,
-						  ts, completed, completed_end);
+						  ts, started, completed);
 			rcutorture_trace_dump();
 		}
 		__this_cpu_inc(rcu_torture_count[pipe_count]);
-		completed = completed_end - completed;
+		completed = completed - started;
+		if (cur_ops->started)
+			completed++;
 		if (completed > RCU_TORTURE_PIPE_LEN) {
 			/* Should not happen, but... */
 			completed = RCU_TORTURE_PIPE_LEN;
···
 		cur_ops->cb_barrier(); /* Implies smp_mb() for wait_event(). */
 		if (atomic_read(&barrier_cbs_invoked) != n_barrier_cbs) {
 			n_rcu_torture_barrier_error++;
+			pr_err("barrier_cbs_invoked = %d, n_barrier_cbs = %d\n",
+			       atomic_read(&barrier_cbs_invoked),
+			       n_barrier_cbs);
 			WARN_ON_ONCE(1);
 		}
 		n_barrier_successes++;

kernel/rcu/srcu.c

···
  * Report the number of batches, correlated with, but not necessarily
  * precisely the same as, the number of grace periods that have elapsed.
  */
-long srcu_batches_completed(struct srcu_struct *sp)
+unsigned long srcu_batches_completed(struct srcu_struct *sp)
 {
 	return sp->completed;
 }

kernel/rcu/tiny.c

···
 		       void (*func)(struct rcu_head *rcu),
 		       struct rcu_ctrlblk *rcp);
 
-static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
-
 #include "tiny_plugin.h"
-
-/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcu/tree.c. */
-static void rcu_idle_enter_common(long long newval)
-{
-	if (newval) {
-		RCU_TRACE(trace_rcu_dyntick(TPS("--="),
-					    rcu_dynticks_nesting, newval));
-		rcu_dynticks_nesting = newval;
-		return;
-	}
-	RCU_TRACE(trace_rcu_dyntick(TPS("Start"),
-				    rcu_dynticks_nesting, newval));
-	if (IS_ENABLED(CONFIG_RCU_TRACE) && !is_idle_task(current)) {
-		struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
-
-		RCU_TRACE(trace_rcu_dyntick(TPS("Entry error: not idle task"),
-					    rcu_dynticks_nesting, newval));
-		ftrace_dump(DUMP_ALL);
-		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
-			  current->pid, current->comm,
-			  idle->pid, idle->comm); /* must be idle task! */
-	}
-	rcu_sched_qs(); /* implies rcu_bh_inc() */
-	barrier();
-	rcu_dynticks_nesting = newval;
-}
 
 /*
  * Enter idle, which is an extended quiescent state if we have fully
- * entered that mode (i.e., if the new value of dynticks_nesting is zero).
+ * entered that mode.
  */
 void rcu_idle_enter(void)
 {
-	unsigned long flags;
-	long long newval;
-
-	local_irq_save(flags);
-	WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
-	if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
-	    DYNTICK_TASK_NEST_VALUE)
-		newval = 0;
-	else
-		newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
-	rcu_idle_enter_common(newval);
-	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_idle_enter);
 
···
  */
 void rcu_irq_exit(void)
 {
-	unsigned long flags;
-	long long newval;
-
-	local_irq_save(flags);
-	newval = rcu_dynticks_nesting - 1;
-	WARN_ON_ONCE(newval < 0);
-	rcu_idle_enter_common(newval);
-	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_irq_exit);
-
-/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcu/tree.c. */
-static void rcu_idle_exit_common(long long oldval)
-{
-	if (oldval) {
-		RCU_TRACE(trace_rcu_dyntick(TPS("++="),
-					    oldval, rcu_dynticks_nesting));
-		return;
-	}
-	RCU_TRACE(trace_rcu_dyntick(TPS("End"), oldval, rcu_dynticks_nesting));
-	if (IS_ENABLED(CONFIG_RCU_TRACE) && !is_idle_task(current)) {
-		struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
-
-		RCU_TRACE(trace_rcu_dyntick(TPS("Exit error: not idle task"),
-			  oldval, rcu_dynticks_nesting));
-		ftrace_dump(DUMP_ALL);
-		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
-			  current->pid, current->comm,
-			  idle->pid, idle->comm); /* must be idle task! */
-	}
-}
 
 /*
  * Exit idle, so that we are no longer in an extended quiescent state.
  */
 void rcu_idle_exit(void)
 {
-	unsigned long flags;
-	long long oldval;
-
-	local_irq_save(flags);
-	oldval = rcu_dynticks_nesting;
-	WARN_ON_ONCE(rcu_dynticks_nesting < 0);
-	if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
-		rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
-	else
-		rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
-	rcu_idle_exit_common(oldval);
-	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_idle_exit);
 
···
  */
 void rcu_irq_enter(void)
 {
-	unsigned long flags;
-	long long oldval;
-
-	local_irq_save(flags);
-	oldval = rcu_dynticks_nesting;
-	rcu_dynticks_nesting++;
-	WARN_ON_ONCE(rcu_dynticks_nesting == 0);
-	rcu_idle_exit_common(oldval);
-	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_irq_enter);
 
···
  */
 bool notrace __rcu_is_watching(void)
 {
-	return rcu_dynticks_nesting;
+	return true;
 }
 EXPORT_SYMBOL(__rcu_is_watching);
 
 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
-
-/*
- * Test whether the current CPU was interrupted from idle.  Nested
- * interrupts don't count, we must be running at the first interrupt
- * level.
- */
-static int rcu_is_cpu_rrupt_from_idle(void)
-{
-	return rcu_dynticks_nesting <= 1;
-}
 
 /*
  * Helper function for rcu_sched_qs() and rcu_bh_qs().
···
 void rcu_check_callbacks(int user)
 {
 	RCU_TRACE(check_cpu_stalls());
-	if (user || rcu_is_cpu_rrupt_from_idle())
+	if (user)
 		rcu_sched_qs();
 	else if (!in_softirq())
 		rcu_bh_qs();
···
 	rcp->curtail = &head->next;
 	RCU_TRACE(rcp->qlen++);
 	local_irq_restore(flags);
+
+	if (unlikely(is_idle_task(current))) {
+		/* force scheduling for rcu_sched_qs() */
+		resched_cpu(0);
+	}
 }
 
 /*
···
 void __init rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+	RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
+	RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
 
 	rcu_early_boot_tests();
 }

kernel/rcu/tiny_plugin.h

···
 	rcp->ticks_this_gp++;
 	j = jiffies;
 	js = ACCESS_ONCE(rcp->jiffies_stall);
-	if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
+	if (rcp->rcucblist && ULONG_CMP_GE(j, js)) {
 		pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
-		       rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
+		       rcp->name, rcp->ticks_this_gp, DYNTICK_TASK_EXIT_IDLE,
 		       jiffies - rcp->gp_start, rcp->qlen);
 		dump_stack();
-	}
-	if (*rcp->curtail && ULONG_CMP_GE(j, js))
 		ACCESS_ONCE(rcp->jiffies_stall) = jiffies +
 			3 * rcu_jiffies_till_stall_check() + 3;
-	else if (ULONG_CMP_GE(j, js))
+	} else if (ULONG_CMP_GE(j, js)) {
 		ACCESS_ONCE(rcp->jiffies_stall) = jiffies + rcu_jiffies_till_stall_check();
+	}
 }
 
 static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)

kernel/rcu/tree.c

···
 static void invoke_rcu_core(void);
 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
 
+/* rcuc/rcub kthread realtime priority */
+static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
+module_param(kthread_prio, int, 0644);
+
 /*
  * Track the rcutorture test sequence number and the update version
  * number within a given test.  The rcutorture_testseq is incremented
···
 	.dynticks_idle = ATOMIC_INIT(1),
 #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
 };
+
+DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
+EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
 
 /*
  * Let the RCU core know that this CPU has gone through the scheduler,
···
 }
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
+/*
+ * Register a quiesecent state for all RCU flavors.  If there is an
+ * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
+ * dyntick-idle quiescent state visible to other CPUs (but only for those
+ * RCU flavors in desparate need of a quiescent state, which will normally
+ * be none of them).  Either way, do a lightweight quiescent state for
+ * all RCU flavors.
+ */
+void rcu_all_qs(void)
+{
+	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
+		rcu_momentary_dyntick_idle();
+	this_cpu_inc(rcu_qs_ctr);
+}
+EXPORT_SYMBOL_GPL(rcu_all_qs);
+
 static long blimit = 10;	/* Maximum callbacks per rcu_do_batch. */
 static long qhimark = 10000;	/* If this many pending, ignore blimit. */
 static long qlowmark = 100;	/* Once only this many pending, use blimit. */
···
 static int rcu_pending(void);
 
 /*
- * Return the number of RCU-sched batches processed thus far for debug & stats.
+ * Return the number of RCU batches started thus far for debug & stats.
  */
-long rcu_batches_completed_sched(void)
+unsigned long rcu_batches_started(void)
+{
+	return rcu_state_p->gpnum;
+}
+EXPORT_SYMBOL_GPL(rcu_batches_started);
+
+/*
+ * Return the number of RCU-sched batches started thus far for debug & stats.
+ */
+unsigned long rcu_batches_started_sched(void)
+{
+	return rcu_sched_state.gpnum;
+}
+EXPORT_SYMBOL_GPL(rcu_batches_started_sched);
+
+/*
+ * Return the number of RCU BH batches started thus far for debug & stats.
+ */
+unsigned long rcu_batches_started_bh(void)
+{
+	return rcu_bh_state.gpnum;
+}
+EXPORT_SYMBOL_GPL(rcu_batches_started_bh);
+
+/*
+ * Return the number of RCU batches completed thus far for debug & stats.
+ */
+unsigned long rcu_batches_completed(void)
+{
+	return rcu_state_p->completed;
+}
+EXPORT_SYMBOL_GPL(rcu_batches_completed);
+
+/*
+ * Return the number of RCU-sched batches completed thus far for debug & stats.
+ */
+unsigned long rcu_batches_completed_sched(void)
 {
 	return rcu_sched_state.completed;
 }
 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
 
 /*
- * Return the number of RCU BH batches processed thus far for debug & stats.
+ * Return the number of RCU BH batches completed thus far for debug & stats.
  */
-long rcu_batches_completed_bh(void)
+unsigned long rcu_batches_completed_bh(void)
 {
 	return rcu_bh_state.completed;
 }
···
 /**
  * rcu_nmi_enter - inform RCU of entry to NMI context
  *
- * If the CPU was idle with dynamic ticks active, and there is no
- * irq handler running, this updates rdtp->dynticks_nmi to let the
- * RCU grace-period handling know that the CPU is active.
+ * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
+ * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
+ * that the CPU is active.  This implementation permits nested NMIs, as
+ * long as the nesting level does not overflow an int.  (You will probably
+ * run out of stack space first.)
  */
 void rcu_nmi_enter(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+	int incby = 2;
 
-	if (rdtp->dynticks_nmi_nesting == 0 &&
-	    (atomic_read(&rdtp->dynticks) & 0x1))
-		return;
-	rdtp->dynticks_nmi_nesting++;
-	smp_mb__before_atomic();  /* Force delay from prior write. */
-	atomic_inc(&rdtp->dynticks);
-	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
-	smp_mb__after_atomic();  /* See above. */
-	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+	/* Complain about underflow. */
+	WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
+
+	/*
+	 * If idle from RCU viewpoint, atomically increment ->dynticks
+	 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
+	 * Otherwise, increment ->dynticks_nmi_nesting by two.  This means
+	 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
+	 * to be in the outermost NMI handler that interrupted an RCU-idle
+	 * period (observation due to Andy Lutomirski).
+	 */
+	if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
+		smp_mb__before_atomic();  /* Force delay from prior write. */
+		atomic_inc(&rdtp->dynticks);
+		/* atomic_inc() before later RCU read-side crit sects */
+		smp_mb__after_atomic();  /* See above. */
+		WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+		incby = 1;
+	}
+	rdtp->dynticks_nmi_nesting += incby;
+	barrier();
 }
 
 /**
  * rcu_nmi_exit - inform RCU of exit from NMI context
  *
- * If the CPU was idle with dynamic ticks active, and there is no
- * irq handler running, this updates rdtp->dynticks_nmi to let the
- * RCU grace-period handling know that the CPU is no longer active.
+ * If we are returning from the outermost NMI handler that interrupted an
+ * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
+ * to let the RCU grace-period handling know that the CPU is back to
+ * being RCU-idle.
  */
 void rcu_nmi_exit(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
 
-	if (rdtp->dynticks_nmi_nesting == 0 ||
-	    --rdtp->dynticks_nmi_nesting != 0)
+	/*
+	 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
+	 * (We are exiting an NMI handler, so RCU better be paying attention
+	 * to us!)
+	 */
+	WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
+	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+
+	/*
+	 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
+	 * leave it in non-RCU-idle state.
+	 */
+	if (rdtp->dynticks_nmi_nesting != 1) {
+		rdtp->dynticks_nmi_nesting -= 2;
 		return;
+	}
+
+	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
+	rdtp->dynticks_nmi_nesting = 0;
 	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
 	smp_mb__before_atomic();  /* See above. */
 	atomic_inc(&rdtp->dynticks);
···
 		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
 		return 1;
 	} else {
+		if (ULONG_CMP_LT(ACCESS_ONCE(rdp->gpnum) + ULONG_MAX / 4,
+				 rdp->mynode->gpnum))
+			ACCESS_ONCE(rdp->gpwrap) = true;
 		return 0;
 	}
 }
-
-/*
- * This function really isn't for public consumption, but RCU is special in
- * that context switches can allow the state machine to make progress.
- */
-extern void resched_cpu(int cpu);
 
 /*
  * Return true if the specified CPU has passed through a quiescent
···
 	j1 = rcu_jiffies_till_stall_check();
 	ACCESS_ONCE(rsp->jiffies_stall) = j + j1;
 	rsp->jiffies_resched = j + j1 / 2;
+	rsp->n_force_qs_gpstart = ACCESS_ONCE(rsp->n_force_qs);
+}
+
+/*
+ * Complain about starvation of grace-period kthread.
+ */
+static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
+{
+	unsigned long gpa;
+	unsigned long j;
+
+	j = jiffies;
+	gpa = ACCESS_ONCE(rsp->gp_activity);
+	if (j - gpa > 2 * HZ)
+		pr_err("%s kthread starved for %ld jiffies!\n",
+		       rsp->name, j - gpa);
 }
 
 /*
···
 	}
 }
 
-static void print_other_cpu_stall(struct rcu_state *rsp)
+static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 {
 	int cpu;
 	long delta;
 	unsigned long flags;
+	unsigned long gpa;
+	unsigned long j;
 	int ndetected = 0;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 	long totqlen = 0;
···
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	}
 
-	/*
-	 * Now rat on any tasks that got kicked up to the root rcu_node
-	 * due to CPU offlining.
-	 */
-	rnp = rcu_get_root(rsp);
-	raw_spin_lock_irqsave(&rnp->lock, flags);
-	ndetected += rcu_print_task_stall(rnp);
-	raw_spin_unlock_irqrestore(&rnp->lock, flags);
-
 	print_cpu_stall_info_end();
 	for_each_possible_cpu(cpu)
 		totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
 	pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
 	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
 	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
-	if (ndetected == 0)
-		pr_err("INFO: Stall ended before state dump start\n");
-	else
+	if (ndetected) {
 		rcu_dump_cpu_stacks(rsp);
+	} else {
+		if (ACCESS_ONCE(rsp->gpnum) != gpnum ||
+		    ACCESS_ONCE(rsp->completed) == gpnum) {
+			pr_err("INFO: Stall ended before state dump start\n");
+		} else {
+			j = jiffies;
+			gpa = ACCESS_ONCE(rsp->gp_activity);
+			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld\n",
+			       rsp->name, j - gpa, j, gpa,
+			       jiffies_till_next_fqs);
+			/* In this case, the current CPU might be at fault. */
+			sched_show_task(current);
+		}
+	}
 
 	/* Complain about tasks blocking the grace period. */
-
 	rcu_print_detail_task_stall(rsp);
+
+	rcu_check_gp_kthread_starvation(rsp);
 
 	force_quiescent_state(rsp);  /* Kick them all. */
 }
···
 	pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
 		jiffies - rsp->gp_start,
 		(long)rsp->gpnum, (long)rsp->completed, totqlen);
+
+	rcu_check_gp_kthread_starvation(rsp);
+
 	rcu_dump_cpu_stacks(rsp);
 
 	raw_spin_lock_irqsave(&rnp->lock, flags);
···
 		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
 
 		/* They had a few time units to dump stack, so complain. */
-		print_other_cpu_stall(rsp);
+		print_other_cpu_stall(rsp, gpnum);
 	}
 }
 
···
 	bool ret;
 
 	/* Handle the ends of any preceding grace periods first. */
-	if (rdp->completed == rnp->completed) {
+	if (rdp->completed == rnp->completed &&
+	    !unlikely(ACCESS_ONCE(rdp->gpwrap))) {
 
 		/* No grace period end, so just accelerate recent callbacks. */
 		ret = rcu_accelerate_cbs(rsp, rnp, rdp);
···
 		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
 	}
 
-	if (rdp->gpnum != rnp->gpnum) {
+	if (rdp->gpnum != rnp->gpnum || unlikely(ACCESS_ONCE(rdp->gpwrap))) {
 		/*
 		 * If the current grace period is waiting for this CPU,
 		 * set up to detect a quiescent state, otherwise don't
···
 		rdp->gpnum = rnp->gpnum;
 		trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
 		rdp->passed_quiesce = 0;
+		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
 		rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
 		zero_cpu_stall_ticks(rdp);
+		ACCESS_ONCE(rdp->gpwrap) = false;
 	}
 	return ret;
 }
···
 	local_irq_save(flags);
 	rnp = rdp->mynode;
 	if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
-	     rdp->completed == ACCESS_ONCE(rnp->completed)) || /* w/out lock. */
+	     rdp->completed == ACCESS_ONCE(rnp->completed) &&
+	     !unlikely(ACCESS_ONCE(rdp->gpwrap))) || /* w/out lock. */
 	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
 		local_irq_restore(flags);
 		return;
···
 	struct rcu_data *rdp;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
+	ACCESS_ONCE(rsp->gp_activity) = jiffies;
 	rcu_bind_gp_kthread();
 	raw_spin_lock_irq(&rnp->lock);
 	smp_mb__after_unlock_lock();
···
 					    rnp->grphi, rnp->qsmask);
 		raw_spin_unlock_irq(&rnp->lock);
 		cond_resched_rcu_qs();
+		ACCESS_ONCE(rsp->gp_activity) = jiffies;
 	}
 
 	mutex_unlock(&rsp->onoff_mutex);
···
 	unsigned long maxj;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
+	ACCESS_ONCE(rsp->gp_activity) = jiffies;
 	rsp->n_force_qs++;
 	if (fqs_state == RCU_SAVE_DYNTICK) {
 		/* Collect dyntick-idle snapshots. */
···
 	struct rcu_data *rdp;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
+	ACCESS_ONCE(rsp->gp_activity) = jiffies;
 	raw_spin_lock_irq(&rnp->lock);
 	smp_mb__after_unlock_lock();
 	gp_duration = jiffies - rsp->gp_start;
···
 		nocb += rcu_future_gp_cleanup(rsp, rnp);
 		raw_spin_unlock_irq(&rnp->lock);
 		cond_resched_rcu_qs();
+		ACCESS_ONCE(rsp->gp_activity) = jiffies;
 	}
 	rnp = rcu_get_root(rsp);
 	raw_spin_lock_irq(&rnp->lock);
···
 			if (rcu_gp_init(rsp))
 				break;
 			cond_resched_rcu_qs();
+			ACCESS_ONCE(rsp->gp_activity) = jiffies;
 			WARN_ON(signal_pending(current));
 			trace_rcu_grace_period(rsp->name,
 					       ACCESS_ONCE(rsp->gpnum),
···
 						       ACCESS_ONCE(rsp->gpnum),
 						       TPS("fqsend"));
 				cond_resched_rcu_qs();
+				ACCESS_ONCE(rsp->gp_activity) = jiffies;
 			} else {
 				/* Deal with stray signal. */
 				cond_resched_rcu_qs();
+				ACCESS_ONCE(rsp->gp_activity) = jiffies;
 				WARN_ON(signal_pending(current));
 				trace_rcu_grace_period(rsp->name,
 						       ACCESS_ONCE(rsp->gpnum),
···
 	rnp = rdp->mynode;
 	raw_spin_lock_irqsave(&rnp->lock, flags);
 	smp_mb__after_unlock_lock();
-	if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
-	    rnp->completed == rnp->gpnum) {
+	if ((rdp->passed_quiesce == 0 &&
+	     rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) ||
+	    rdp->gpnum != rnp->gpnum || rnp->completed == rnp->gpnum ||
+	    rdp->gpwrap) {
 
 		/*
 		 * The grace period in which this quiescent state was
···
 		 * within the current grace period.
 		 */
 		rdp->passed_quiesce = 0;	/* need qs for new gp. */
+		rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 		return;
 	}
···
 	 * Was there a quiescent state since the beginning of the grace
 	 * period? If no, then exit and wait for the next call.
 	 */
-	if (!rdp->passed_quiesce)
+	if (!rdp->passed_quiesce &&
+	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr))
 		return;
 
 	/*
···
 }
 
 /*
+ * All CPUs for the specified rcu_node structure have gone offline,
+ * and all tasks that were preempted within an RCU read-side critical
+ * section while running on one of those CPUs have since exited their RCU
+ * read-side critical section.  Some other CPU is reporting this fact with
+ * the specified rcu_node structure's ->lock held and interrupts disabled.
+ * This function therefore goes up the tree of rcu_node structures,
+ * clearing the corresponding bits in the ->qsmaskinit fields.  Note that
+ * the leaf rcu_node structure's ->qsmaskinit field has already been
+ * updated
+ *
+ * This function does check that the specified rcu_node structure has
+ * all CPUs offline and no blocked tasks, so it is OK to invoke it
+ * prematurely.  That said, invoking it after the fact will cost you
+ * a needless lock acquisition.  So once it has done its work, don't
+ * invoke it again.
+ */
+static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
+{
+	long mask;
+	struct rcu_node *rnp = rnp_leaf;
+
+	if (rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
+		return;
+	for (;;) {
+		mask = rnp->grpmask;
+		rnp = rnp->parent;
+		if (!rnp)
+			break;
+		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+		smp_mb__after_unlock_lock(); /* GP memory ordering. */
+		rnp->qsmaskinit &= ~mask;
+		if (rnp->qsmaskinit) {
+			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+			return;
+		}
+		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+	}
+}
+
+/*
  * The CPU has been completely removed, and some other CPU is reporting
  * this fact from process context.  Do the remainder of the cleanup,
  * including orphaning the outgoing CPU's RCU callbacks, and also
···
 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 {
 	unsigned long flags;
-	unsigned long mask;
-	int need_report = 0;
 	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
 	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
 
···
 	/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
 	rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
 	rcu_adopt_orphan_cbs(rsp, flags);
+	raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
 
-	/* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
-	mask = rdp->grpmask;	/* rnp->grplo is constant. */
-	do {
-		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
-		smp_mb__after_unlock_lock();
-		rnp->qsmaskinit &= ~mask;
-		if (rnp->qsmaskinit != 0) {
-			if (rnp != rdp->mynode)
-				raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
-			break;
-		}
-		if (rnp == rdp->mynode)
-			need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
-		else
-			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
-		mask = rnp->grpmask;
-		rnp = rnp->parent;
-	} while (rnp != NULL);
-
-	/*
-	 * We still hold the leaf rcu_node structure lock here, and
-	 * irqs are still disabled.  The reason for this subterfuge is
-	 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
-	 * held leads to deadlock.
-	 */
-	raw_spin_unlock(&rsp->orphan_lock); /* irqs remain disabled. */
-	rnp = rdp->mynode;
-	if (need_report & RCU_OFL_TASKS_NORM_GP)
-		rcu_report_unblock_qs_rnp(rnp, flags);
-	else
-		raw_spin_unlock_irqrestore(&rnp->lock, flags);
-	if (need_report & RCU_OFL_TASKS_EXP_GP)
-		rcu_report_exp_rnp(rsp, rnp, true);
+	/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
+	raw_spin_lock_irqsave(&rnp->lock, flags);
+	smp_mb__after_unlock_lock();	/* Enforce GP memory-order guarantee. */
+	rnp->qsmaskinit &= ~rdp->grpmask;
+	if (rnp->qsmaskinit == 0 && !rcu_preempt_has_tasks(rnp))
+		rcu_cleanup_dead_rnp(rnp);
+	rcu_report_qs_rnp(rdp->grpmask, rsp, rnp, flags); /* Rlses rnp->lock. */
 	WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
 		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
 		  cpu, rdp->qlen, rdp->nxtlist);
···
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
 
 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
+{
+}
+
+static void __maybe_unused rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
 {
 }
 
···
 		}
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	}
-	rnp = rcu_get_root(rsp);
-	if (rnp->qsmask == 0) {
-		raw_spin_lock_irqsave(&rnp->lock, flags);
-		smp_mb__after_unlock_lock();
-		rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
-	}
 }
 
 /*
···
  * Schedule RCU callback invocation.  If the specified type of RCU
  * does not support RCU priority boosting, just do a direct call,
  * otherwise wake up the per-CPU kernel kthread.  Note that because we
- * are running on the current CPU with interrupts disabled, the
+ * are running on the current CPU with softirqs disabled, the
  * rcu_cpu_kthread_task cannot disappear out from under us.
  */
 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
···
 
 	/* Is the RCU core waiting for a quiescent state from this CPU? */
 	if (rcu_scheduler_fully_active &&
-	    rdp->qs_pending && !rdp->passed_quiesce) {
+	    rdp->qs_pending && !rdp->passed_quiesce &&
+	    rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
 		rdp->n_rp_qs_pending++;
-	} else if (rdp->qs_pending && rdp->passed_quiesce) {
+	} else if (rdp->qs_pending &&
+		   (rdp->passed_quiesce ||
+		    rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) {
 		rdp->n_rp_report_qs++;
 		return 1;
 	}
···
 	}
 
 	/* Has a new RCU grace period started? */
-	if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
+	if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum ||
+	    unlikely(ACCESS_ONCE(rdp->gpwrap))) { /* outside lock */
 		rdp->n_rp_gp_started++;
 		return 1;
 	}
···
 			} else {
 				_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
 						   rsp->n_barrier_done);
+				smp_mb__before_atomic();
 				atomic_inc(&rsp->barrier_cpu_count);
 				__call_rcu(&rdp->barrier_head,
 					   rcu_barrier_callback, rsp, cpu, 0);
···
 	/* Set up local state, ensuring consistent view of global state. */
 	raw_spin_lock_irqsave(&rnp->lock, flags);
 	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
-	init_callback_list(rdp);
-	rdp->qlen_lazy = 0;
-	ACCESS_ONCE(rdp->qlen) = 0;
 	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
 	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
 	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
···
 			rdp->gpnum = rnp->completed;
 			rdp->completed = rnp->completed;
 			rdp->passed_quiesce = 0;
+			rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
 			rdp->qs_pending = 0;
 			trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
 		}
···
 static int __init rcu_spawn_gp_kthread(void)
 {
 	unsigned long flags;
+	int kthread_prio_in = kthread_prio;
 	struct rcu_node *rnp;
 	struct rcu_state *rsp;
+	struct sched_param sp;
 	struct task_struct *t;
+
+	/* Force priority into range. */
+	if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
+		kthread_prio = 1;
+	else if (kthread_prio < 0)
+		kthread_prio = 0;
+	else if (kthread_prio > 99)
+		kthread_prio = 99;
+	if (kthread_prio != kthread_prio_in)
+		pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
+			 kthread_prio, kthread_prio_in);
 
 	rcu_scheduler_fully_active = 1;
 	for_each_rcu_flavor(rsp) {
-		t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
+		t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
 		BUG_ON(IS_ERR(t));
 		rnp = rcu_get_root(rsp);
 		raw_spin_lock_irqsave(&rnp->lock, flags);
 		rsp->gp_kthread = t;
+		if (kthread_prio) {
+			sp.sched_priority = kthread_prio;
+			sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+		}
+		wake_up_process(t);
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	}
 	rcu_spawn_nocb_kthreads();

kernel/rcu/tree.h

···
 #include <linux/threads.h>
 #include <linux/cpumask.h>
 #include <linux/seqlock.h>
-#include <linux/irq_work.h>
 
 /*
  * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
···
 				/*  queued on this rcu_node structure that */
 				/*  are blocking the current grace period, */
 				/*  there can be no such task. */
-	struct completion boost_completion;
-				/* Used to ensure that the rt_mutex used */
-				/*  to carry out the boosting is fully */
-				/*  released with no future boostee accesses */
-				/*  before that rt_mutex is re-initialized. */
 	struct rt_mutex boost_mtx;
 				/* Used only for the priority-boosting */
 				/*  side effect, not as a lock. */
···
 					/*  in order to detect GP end. */
 	unsigned long	gpnum;		/* Highest gp number that this CPU */
 					/*  is aware of having started. */
+	unsigned long	rcu_qs_ctr_snap;/* Snapshot of rcu_qs_ctr to check */
+					/*  for rcu_all_qs() invocations. */
 	bool		passed_quiesce;	/* User-mode/idle loop etc. */
 	bool		qs_pending;	/* Core waits for quiesc state. */
 	bool		beenonline;	/* CPU online at least once. */
+	bool		gpwrap;		/* Possible gpnum/completed wrap. */
 	struct rcu_node *mynode;	/* This CPU's leaf of hierarchy */
 	unsigned long grpmask;		/* Mask to apply to leaf qsmask. */
 #ifdef CONFIG_RCU_CPU_STALL_INFO
···
 #ifdef CONFIG_RCU_NOCB_CPU
 	struct rcu_head *nocb_head;	/* CBs waiting for kthread. */
 	struct rcu_head **nocb_tail;
-	atomic_long_t nocb_q_count;	/* # CBs waiting for kthread */
-	atomic_long_t nocb_q_count_lazy; /*  (approximate). */
+	atomic_long_t nocb_q_count;	/* # CBs waiting for nocb */
+	atomic_long_t nocb_q_count_lazy; /*  invocation (all stages). */
 	struct rcu_head *nocb_follower_head; /* CBs ready to invoke. */
 	struct rcu_head **nocb_follower_tail;
-	atomic_long_t nocb_follower_count; /* # CBs ready to invoke. */
-	atomic_long_t nocb_follower_count_lazy; /*  (approximate). */
-	int nocb_p_count;		/* # CBs being invoked by kthread */
-	int nocb_p_count_lazy;		/*  (approximate). */
 	wait_queue_head_t nocb_wq;	/* For nocb kthreads to sleep on. */
 	struct task_struct *nocb_kthread;
 	int nocb_defer_wakeup;		/* Defer wakeup of nocb_kthread. */
···
 	struct rcu_head *nocb_gp_head ____cacheline_internodealigned_in_smp;
 					/* CBs waiting for GP. */
 	struct rcu_head **nocb_gp_tail;
-	long nocb_gp_count;
-	long nocb_gp_count_lazy;
 	bool nocb_leader_sleep;		/* Is the nocb leader thread asleep? */
 	struct rcu_data *nocb_next_follower;
 					/* Next follower in wakeup chain. */
···
 						/*  due to no GP active. */
 	unsigned long gp_start;			/* Time at which GP started, */
 						/*  but in jiffies. */
+	unsigned long gp_activity;		/* Time of last GP kthread */
+						/*  activity in jiffies. */
 	unsigned long jiffies_stall;		/* Time at which to check */
 						/*  for CPU stalls. */
 	unsigned long jiffies_resched;		/* Time at which to resched */
 						/*  a reluctant CPU. */
+	unsigned long n_force_qs_gpstart;	/* Snapshot of n_force_qs at */
+						/*  GP start. */
 	unsigned long gp_max;			/* Maximum GP duration in */
 						/*  jiffies. */
 	const char *name;			/* Name of structure. */
···
 /* Sequence through rcu_state structures for each RCU flavor. */
 #define for_each_rcu_flavor(rsp) \
 	list_for_each_entry((rsp), &rcu_struct_flavors, flavors)
-
-/* Return values for rcu_preempt_offline_tasks(). */
-
-#define RCU_OFL_TASKS_NORM_GP	0x1		/* Tasks blocking normal */
-						/*  GP were moved to root. */
-#define RCU_OFL_TASKS_EXP_GP	0x2		/* Tasks blocking expedited */
-						/*  GP were moved to root. */
 
 /*
  * RCU implementation internal declarations:
···
 
 /* Forward declarations for rcutree_plugin.h */
 static void rcu_bootup_announce(void);
-long rcu_batches_completed(void);
 static void rcu_preempt_note_context_switch(void);
 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
 #ifdef CONFIG_HOTPLUG_CPU
-static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
-				      unsigned long flags);
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 static void rcu_print_detail_task_stall(struct rcu_state *rsp);
 static int rcu_print_task_stall(struct rcu_node *rnp);
 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
-#ifdef CONFIG_HOTPLUG_CPU
-static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
-				     struct rcu_node *rnp,
-				     struct rcu_data *rdp);
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
 static void rcu_preempt_check_callbacks(void);
 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
-#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_PREEMPT_RCU)
-static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
-			       bool wake);
-#endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_PREEMPT_RCU) */
 static void __init __rcu_init_preempt(void);
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
···
 #endif /* #ifndef RCU_TREE_NONCORE */
 
 #ifdef CONFIG_RCU_TRACE
+/* Read out queue lengths for tracing. */
+static inline void rcu_nocb_q_lengths(struct rcu_data *rdp, long *ql, long *qll)
+{
 #ifdef CONFIG_RCU_NOCB_CPU
-/* Sum up queue lengths for tracing. */
-static inline void rcu_nocb_q_lengths(struct rcu_data *rdp, long *ql, long *qll)
-{
-	*ql = atomic_long_read(&rdp->nocb_q_count) +
-	      rdp->nocb_p_count +
-	      atomic_long_read(&rdp->nocb_follower_count) +
-	      rdp->nocb_p_count + rdp->nocb_gp_count;
-	*qll = atomic_long_read(&rdp->nocb_q_count_lazy) +
-	       rdp->nocb_p_count_lazy +
-	       atomic_long_read(&rdp->nocb_follower_count_lazy) +
-	       rdp->nocb_p_count_lazy + rdp->nocb_gp_count_lazy;
-}
+	*ql = atomic_long_read(&rdp->nocb_q_count);
+	*qll = atomic_long_read(&rdp->nocb_q_count_lazy);
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
-static inline void rcu_nocb_q_lengths(struct rcu_data *rdp, long *ql, long *qll)
-{
 	*ql = 0;
 	*qll = 0;
-}
 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
+}
 #endif /* #ifdef CONFIG_RCU_TRACE */

kernel/rcu/tree_plugin.h

···
 
 #include "../locking/rtmutex_common.h"
 
-/* rcuc/rcub kthread realtime priority */
-static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
-module_param(kthread_prio, int, 0644);
-
 /*
  * Control variables for per-CPU and per-rcu_node kthreads.  These
  * handle all flavors of RCU.
···
 static struct rcu_state *rcu_state_p = &rcu_preempt_state;
 
 static int rcu_preempted_readers_exp(struct rcu_node *rnp);
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
+			       bool wake);
 
 /*
  * Tell them what RCU they are running.
···
 	pr_info("Preemptible hierarchical RCU implementation.\n");
 	rcu_bootup_announce_oddness();
 }
-
-/*
- * Return the number of RCU-preempt batches processed thus far
- * for debug and statistics.
- */
-static long rcu_batches_completed_preempt(void)
-{
-	return rcu_preempt_state.completed;
-}
-EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
-
-/*
- * Return the number of RCU batches processed thus far for debug & stats.
- */
-long rcu_batches_completed(void)
-{
-	return rcu_batches_completed_preempt();
-}
-EXPORT_SYMBOL_GPL(rcu_batches_completed);
 
 /*
  * Record a preemptible-RCU quiescent state for the specified CPU.  Note
···
 }
 
 /*
+ * Return true if the specified rcu_node structure has tasks that were
+ * preempted within an RCU read-side critical section.
+ */
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
+{
+	return !list_empty(&rnp->blkd_tasks);
+}
+
+/*
  * Handle special cases during rcu_read_unlock(), such as needing to
  * notify RCU core processing or task having blocked during the RCU
  * read-side critical section.
  */
 void rcu_read_unlock_special(struct task_struct *t)
 {
-	int empty;
-	int empty_exp;
-	int empty_exp_now;
+	bool empty;
+	bool empty_exp;
+	bool empty_norm;
+	bool empty_exp_now;
 	unsigned long flags;
 	struct list_head *np;
 #ifdef CONFIG_RCU_BOOST
···
 				break;
 			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
 		}
-		empty = !rcu_preempt_blocked_readers_cgp(rnp);
+		empty = !rcu_preempt_has_tasks(rnp);
+		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
 		empty_exp = !rcu_preempted_readers_exp(rnp);
 		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
 		np = rcu_next_node_entry(t, rnp);
···
 #endif /* #ifdef CONFIG_RCU_BOOST */
 
 		/*
+		 * If this was the last task on the list, go see if we
+		 * need to propagate ->qsmaskinit bit clearing up the
+		 * rcu_node tree.
+		 */
+		if (!empty && !rcu_preempt_has_tasks(rnp))
+			rcu_cleanup_dead_rnp(rnp);
+
+		/*
 		 * If this was the last task on the current list, and if
 		 * we aren't waiting on any CPUs, report the quiescent state.
 		 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
 		 * so we must take a snapshot of the expedited state.
 		 */
 		empty_exp_now = !rcu_preempted_readers_exp(rnp);
-		if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
+		if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
 			trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
 							 rnp->gpnum,
 							 0, rnp->qsmask,
···
 
 #ifdef CONFIG_RCU_BOOST
 		/* Unboost if we were boosted. */
-		if (drop_boost_mutex) {
+		if (drop_boost_mutex)
 			rt_mutex_unlock(&rnp->boost_mtx);
-			complete(&rnp->boost_completion);
-		}
 #endif /* #ifdef CONFIG_RCU_BOOST */
 
 		/*
···
 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
 {
 	WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
-	if (!list_empty(&rnp->blkd_tasks))
+	if (rcu_preempt_has_tasks(rnp))
 		rnp->gp_tasks = rnp->blkd_tasks.next;
 	WARN_ON_ONCE(rnp->qsmask);
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
-
-/*
- * Handle tasklist migration for case in which all CPUs covered by the
- * specified rcu_node have gone offline.  Move them up to the root
- * rcu_node.  The reason for not just moving them to the immediate
- * parent is to remove the need for rcu_read_unlock_special() to
- * make more than two attempts to acquire the target rcu_node's lock.
- * Returns true if there were tasks blocking the current RCU grace
- * period.
- *
- * Returns 1 if there was previously a task blocking the current grace
- * period on the specified rcu_node structure.
- *
- * The caller must hold rnp->lock with irqs disabled.
- */
-static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
-				     struct rcu_node *rnp,
-				     struct rcu_data *rdp)
-{
-	struct list_head *lp;
-	struct list_head *lp_root;
-	int retval = 0;
-	struct rcu_node *rnp_root = rcu_get_root(rsp);
-	struct task_struct *t;
-
-	if (rnp == rnp_root) {
-		WARN_ONCE(1, "Last CPU thought to be offlined?");
-		return 0;  /* Shouldn't happen: at least one CPU online. */
-	}
-
-	/* If we are on an internal node, complain bitterly. */
-	WARN_ON_ONCE(rnp != rdp->mynode);
-
-	/*
-	 * Move tasks up to root rcu_node.  Don't try to get fancy for
-	 * this corner-case operation -- just put this node's tasks
-	 * at the head of the root node's list, and update the root node's
-	 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
-	 * if non-NULL.  This might result in waiting for more tasks than
-	 * absolutely necessary, but this is a good performance/complexity
-	 * tradeoff.
-	 */
-	if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
-		retval |= RCU_OFL_TASKS_NORM_GP;
-	if (rcu_preempted_readers_exp(rnp))
-		retval |= RCU_OFL_TASKS_EXP_GP;
-	lp = &rnp->blkd_tasks;
-	lp_root = &rnp_root->blkd_tasks;
-	while (!list_empty(lp)) {
-		t = list_entry(lp->next, typeof(*t), rcu_node_entry);
-		raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
-		smp_mb__after_unlock_lock();
-		list_del(&t->rcu_node_entry);
-		t->rcu_blocked_node = rnp_root;
-		list_add(&t->rcu_node_entry, lp_root);
-		if (&t->rcu_node_entry == rnp->gp_tasks)
-			rnp_root->gp_tasks = rnp->gp_tasks;
-		if (&t->rcu_node_entry == rnp->exp_tasks)
-			rnp_root->exp_tasks = rnp->exp_tasks;
-#ifdef CONFIG_RCU_BOOST
-		if (&t->rcu_node_entry == rnp->boost_tasks)
-			rnp_root->boost_tasks = rnp->boost_tasks;
-#endif /* #ifdef CONFIG_RCU_BOOST */
-		raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
-	}
-
-	rnp->gp_tasks = NULL;
-	rnp->exp_tasks = NULL;
-#ifdef CONFIG_RCU_BOOST
-	rnp->boost_tasks = NULL;
-	/*
-	 * In case root is being boosted and leaf was not.  Make sure
-	 * that we boost the tasks blocking the current grace period
-	 * in this case.
-	 */
-	raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
-	smp_mb__after_unlock_lock();
-	if (rnp_root->boost_tasks != NULL &&
-	    rnp_root->boost_tasks != rnp_root->gp_tasks &&
-	    rnp_root->boost_tasks != rnp_root->exp_tasks)
-		rnp_root->boost_tasks = rnp_root->gp_tasks;
-	raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
-	return retval;
-}
 
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 
···
 
 	raw_spin_lock_irqsave(&rnp->lock, flags);
 	smp_mb__after_unlock_lock();
-	if (list_empty(&rnp->blkd_tasks)) {
+	if (!rcu_preempt_has_tasks(rnp)) {
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	} else {
 		rnp->exp_tasks = rnp->blkd_tasks.next;
···
 }
 
 /*
- * Return the number of RCU batches processed thus far for debug & stats.
- */
-long rcu_batches_completed(void)
-{
-	return rcu_batches_completed_sched();
-}
-EXPORT_SYMBOL_GPL(rcu_batches_completed);
-
-/*
  * Because preemptible RCU does not exist, we never have to check for
  * CPUs being in quiescent states.
  */
···
 
 #ifdef CONFIG_HOTPLUG_CPU
 
-/* Because preemptible RCU does not exist, no quieting of tasks. */
-static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
-	__releases(rnp->lock)
+/*
+ * Because there is no preemptible RCU, there can be no readers blocked.
+ */
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
 {
-	raw_spin_unlock_irqrestore(&rnp->lock, flags);
+	return false;
 }
 
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
···
 	WARN_ON_ONCE(rnp->qsmask);
 }
 
-#ifdef CONFIG_HOTPLUG_CPU
-
-/*
- * Because preemptible RCU does not exist, it never needs to migrate
- * tasks that were blocked within RCU read-side critical sections, and
- * such non-existent tasks cannot possibly have been blocking the current
- * grace period.
- */
-static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
-				     struct rcu_node *rnp,
-				     struct rcu_data *rdp)
-{
-	return 0;
-}
-
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-
 /*
  * Because preemptible RCU does not exist, it never has any callbacks
  * to check.
···
 	synchronize_sched_expedited();
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
-
-#ifdef CONFIG_HOTPLUG_CPU
-
-/*
- * Because preemptible RCU does not exist, there is never any need to
- * report on tasks preempted in RCU read-side critical sections during
- * expedited RCU grace periods.
- */
-static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
-			       bool wake)
-{
-}
-
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
 
 /*
  * Because preemptible RCU does not exist, rcu_barrier() is just
···
 
 static void rcu_initiate_boost_trace(struct rcu_node *rnp)
 {
-	if (list_empty(&rnp->blkd_tasks))
+	if (!rcu_preempt_has_tasks(rnp))
 		rnp->n_balk_blkd_tasks++;
 	else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
 		rnp->n_balk_exp_gp_tasks++;
···
 	struct task_struct *t;
 	struct list_head *tb;
 
-	if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
+	if (ACCESS_ONCE(rnp->exp_tasks) == NULL &&
+	    ACCESS_ONCE(rnp->boost_tasks) == NULL)
 		return 0;  /* Nothing left to boost. */
 
 	raw_spin_lock_irqsave(&rnp->lock, flags);
···
 	 */
 	t = container_of(tb, struct task_struct, rcu_node_entry);
 	rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
-	init_completion(&rnp->boost_completion);
 	raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	/* Lock only for side effect: boosts task t's priority. */
 	rt_mutex_lock(&rnp->boost_mtx);
 	rt_mutex_unlock(&rnp->boost_mtx);  /* Then keep lockdep happy. */
-
-	/* Wait for boostee to be done w/boost_mtx before reinitializing. */
-	wait_for_completion(&rnp->boost_completion);
 
 	return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
 	       ACCESS_ONCE(rnp->boost_tasks) != NULL;
···
 	for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
 		if ((mask & 0x1) && cpu != outgoingcpu)
 			cpumask_set_cpu(cpu, cm);
-	if (cpumask_weight(cm) == 0) {
+	if (cpumask_weight(cm) == 0)
 		cpumask_setall(cm);
-		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
-			cpumask_clear_cpu(cpu, cm);
-		WARN_ON_ONCE(cpumask_weight(cm) == 0);
-	}
 	set_cpus_allowed_ptr(t, cm);
 	free_cpumask_var(cm);
 }
···
 	for_each_possible_cpu(cpu)
 		per_cpu(rcu_cpu_has_work, cpu) = 0;
 	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
-	rnp = rcu_get_root(rcu_state_p);
-	(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
-	if (NUM_RCU_NODES > 1) {
-		rcu_for_each_leaf_node(rcu_state_p, rnp)
-			(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
-	}
+	rcu_for_each_leaf_node(rcu_state_p, rnp)
+		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
 }
 
 static void rcu_prepare_kthreads(int cpu)
···
 		 * completed since we last checked and there are
 		 * callbacks not yet ready to invoke.
 		 */
-		if (rdp->completed != rnp->completed &&
+		if ((rdp->completed != rnp->completed ||
+		     unlikely(ACCESS_ONCE(rdp->gpwrap))) &&
 		    rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
 			note_gp_changes(rsp, rdp);
 
···
 		ticks_value = rsp->gpnum - rdp->gpnum;
 	}
 	print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
-	pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
+	pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
 	       cpu, ticks_value, ticks_title,
 	       atomic_read(&rdtp->dynticks) & 0xfff,
 	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
 	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
+	       ACCESS_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
 	       fast_no_hz);
 }
 
···
 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
 {
 	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+	unsigned long ret;
+#ifdef CONFIG_PROVE_RCU
 	struct rcu_head *rhp;
+#endif /* #ifdef CONFIG_PROVE_RCU */
 
-	/* No-CBs CPUs might have callbacks on any of three lists. */
+	/*
+	 * Check count of all no-CBs callbacks awaiting invocation.
+	 * There needs to be a barrier before this function is called,
+	 * but associated with a prior determination that no more
+	 * callbacks would be posted.  In the worst case, the first
+	 * barrier in _rcu_barrier() suffices (but the caller cannot
+	 * necessarily rely on this, not a substitute for the caller
+	 * getting the concurrency design right!).  There must also be
+	 * a barrier between the following load an posting of a callback
+	 * (if a callback is in fact needed).  This is associated with an
+	 * atomic_inc() in the caller.
+	 */
+	ret = atomic_long_read(&rdp->nocb_q_count);
+
+#ifdef CONFIG_PROVE_RCU
 	rhp = ACCESS_ONCE(rdp->nocb_head);
 	if (!rhp)
 		rhp = ACCESS_ONCE(rdp->nocb_gp_head);
···
 		       cpu, rhp->func);
 		WARN_ON_ONCE(1);
 	}
+#endif /* #ifdef CONFIG_PROVE_RCU */
 
-	return !!rhp;
+	return !!ret;
 }
 
 /*
···
 	struct task_struct *t;
 
 	/* Enqueue the callback on the nocb list and update counts. */
+	atomic_long_add(rhcount, &rdp->nocb_q_count);
+	/* rcu_barrier() relies on ->nocb_q_count add before xchg. */
 	old_rhpp = xchg(&rdp->nocb_tail, rhtp);
 	ACCESS_ONCE(*old_rhpp) = rhp;
-	atomic_long_add(rhcount, &rdp->nocb_q_count);
 	atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
 	smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
 
···
 		/* Move callbacks to wait-for-GP list, which is empty. */
 		ACCESS_ONCE(rdp->nocb_head) = NULL;
 		rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
-		rdp->nocb_gp_count = atomic_long_xchg(&rdp->nocb_q_count, 0);
-		rdp->nocb_gp_count_lazy =
-			atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
 		gotcbs = true;
 	}
 
···
 		/* Append callbacks to follower's "done" list. */
 		tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
 		*tail = rdp->nocb_gp_head;
-		atomic_long_add(rdp->nocb_gp_count, &rdp->nocb_follower_count);
-		atomic_long_add(rdp->nocb_gp_count_lazy,
-				&rdp->nocb_follower_count_lazy);
 		smp_mb__after_atomic(); /* Store *tail before wakeup. */
 		if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
 			/*
···
 		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
 		ACCESS_ONCE(rdp->nocb_follower_head) = NULL;
 		tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
-		c = atomic_long_xchg(&rdp->nocb_follower_count, 0);
-		cl = atomic_long_xchg(&rdp->nocb_follower_count_lazy, 0);
-		rdp->nocb_p_count += c;
-		rdp->nocb_p_count_lazy += cl;
 
 		/* Each pass through the following loop invokes a callback. */
-		trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
+		trace_rcu_batch_start(rdp->rsp->name,
+				      atomic_long_read(&rdp->nocb_q_count_lazy),
+				      atomic_long_read(&rdp->nocb_q_count), -1);
 		c = cl = 0;
 		while (list) {
 			next = list->next;
···
 			list = next;
 		}
 		trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
-		ACCESS_ONCE(rdp->nocb_p_count) = rdp->nocb_p_count - c;
-		ACCESS_ONCE(rdp->nocb_p_count_lazy) =
-						rdp->nocb_p_count_lazy - cl;
+		smp_mb__before_atomic();  /* _add after CB invocation. */
+		atomic_long_add(-c, &rdp->nocb_q_count);
+		atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
 		rdp->n_nocbs_invoked += c;
 	}
 	return 0;

kernel/rcu/tree_trace.c

···
 #define RCU_TREE_NONCORE
 #include "tree.h"
 
+DECLARE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
+
 static int r_open(struct inode *inode, struct file *file,
 					const struct seq_operations *op)
 {
···
 
 	if (!rdp->beenonline)
 		return;
-	seq_printf(m, "%3d%cc=%ld g=%ld pq=%d qp=%d",
+	seq_printf(m, "%3d%cc=%ld g=%ld pq=%d/%d qp=%d",
 		   rdp->cpu,
 		   cpu_is_offline(rdp->cpu) ? '!' : ' ',
 		   ulong2long(rdp->completed), ulong2long(rdp->gpnum),
-		   rdp->passed_quiesce, rdp->qs_pending);
+		   rdp->passed_quiesce,
+		   rdp->rcu_qs_ctr_snap == per_cpu(rcu_qs_ctr, rdp->cpu),
+		   rdp->qs_pending);
 	seq_printf(m, " dt=%d/%llx/%d df=%lu",
 		   atomic_read(&rdp->dynticks->dynticks),
 		   rdp->dynticks->dynticks_nesting,

kernel/softirq.c

···
 		 * in the task stack here.
 		 */
 		__do_softirq();
-		rcu_note_context_switch();
 		local_irq_enable();
-		cond_resched();
+		cond_resched_rcu_qs();
 		return;
 	}
 	local_irq_enable();

lib/Kconfig.debug

···
 	tristate "torture tests for RCU"
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
+	select SRCU
 	default n
 	help
 	  This option provides a kernel module that runs torture tests
···
 config RCU_CPU_STALL_INFO
 	bool "Print additional diagnostics on RCU CPU stall"
 	depends on (TREE_RCU || PREEMPT_RCU) && DEBUG_KERNEL
-	default n
+	default y
 	help
 	  For each stalled CPU that is aware of the current RCU grace
 	  period, print out additional per-CPU diagnostic information

mm/Kconfig

···
 
 config MMU_NOTIFIER
 	bool
+	select SRCU
 
 config KSM
 	bool "Enable KSM for page merging"

security/tomoyo/Kconfig

···
 	select SECURITYFS
 	select SECURITY_PATH
 	select SECURITY_NETWORK
+	select SRCU
 	default n
 	help
 	  This selects TOMOYO Linux, pathname-based access control.

tools/testing/selftests/rcutorture/bin/cpus2use.sh

···
 
 ncpus=`grep '^processor' /proc/cpuinfo | wc -l`
 idlecpus=`mpstat | tail -1 | \
-	awk -v ncpus=$ncpus '{ print ncpus * ($7 + $12) / 100 }'`
+	awk -v ncpus=$ncpus '{ print ncpus * ($7 + $NF) / 100 }'`
 awk -v ncpus=$ncpus -v idlecpus=$idlecpus < /dev/null '
 BEGIN {
 	cpus2use = idlecpus;

tools/testing/selftests/rcutorture/bin/kvm-recheck-rcu.sh

···
 	echo Unreadable results directory: $i
 	exit 1
 fi
+. tools/testing/selftests/rcutorture/bin/functions.sh
 
 configfile=`echo $i | sed -e 's/^.*\///'`
 ngps=`grep ver: $i/console.log 2> /dev/null | tail -1 | sed -e 's/^.* ver: //' -e 's/ .*$//'`
···
 		title="$title ($ngpsps per second)"
 	fi
 	echo $title
+	nclosecalls=`grep --binary-files=text 'torture: Reader Batch' $i/console.log | tail -1 | awk '{for (i=NF-8;i<=NF;i++) sum+=$i; } END {print sum}'`
+	if test -z "$nclosecalls"
+	then
+		exit 0
+	fi
+	if test "$nclosecalls" -eq 0
+	then
+		exit 0
+	fi
+	# Compute number of close calls per tenth of an hour
+	nclosecalls10=`awk -v nclosecalls=$nclosecalls -v dur=$dur 'BEGIN { print int(nclosecalls * 36000 / dur) }' < /dev/null`
+	if test $nclosecalls10 -gt 5 -a $nclosecalls -gt 1
+	then
+		print_bug $nclosecalls "Reader Batch close calls in" $(($dur/60)) minute run: $i
+	else
+		print_warning $nclosecalls "Reader Batch close calls in" $(($dur/60)) minute run: $i
+	fi
 fi

tools/testing/selftests/rcutorture/bin/kvm-test-1-run.sh

···
 #
 # Usage: kvm-test-1-run.sh config builddir resdir minutes qemu-args boot_args
 #
-# qemu-args defaults to "-nographic", along with arguments specifying the
-#			number of CPUs and other options generated from
-#			the underlying CPU architecture.
+# qemu-args defaults to "-enable-kvm -soundhw pcspk -nographic", along with
+#			arguments specifying the number of CPUs and other
+#			options generated from the underlying CPU architecture.
 # boot_args defaults to value returned by the per_version_boot_params
 #			shell function.
 #
···
 fi
 
 # Generate -smp qemu argument.
-qemu_args="-nographic $qemu_args"
+qemu_args="-enable-kvm -soundhw pcspk -nographic $qemu_args"
 cpu_count=`configNR_CPUS.sh $config_template`
 cpu_count=`configfrag_boot_cpus "$boot_args" "$config_template" "$cpu_count"`
 vcpus=`identify_qemu_vcpus`
···
 	touch $resdir/buildonly
 	exit 0
 fi
+echo "NOTE: $QEMU either did not run or was interactive" > $builddir/console.log
 echo $QEMU $qemu_args -m 512 -kernel $resdir/bzImage -append \"$qemu_append $boot_args\" > $resdir/qemu-cmd
 ( $QEMU $qemu_args -m 512 -kernel $resdir/bzImage -append "$qemu_append $boot_args"; echo $? > $resdir/qemu-retval ) &
 qemu_pid=$!

tools/testing/selftests/rcutorture/bin/parse-build.sh

···
 #
 # Authors: Paul E. McKenney <[e-mail]>
 
-T=$1
+F=$1
 title=$2
+T=/tmp/parse-build.sh.$$
+trap 'rm -rf $T' 0
+mkdir $T
 
 . functions.sh
 
-if grep -q CC < $T
+if grep -q CC < $F
 then
 	:
 else
···
 	exit 1
 fi
 
-if grep -q "error:" < $T
+if grep -q "error:" < $F
 then
 	print_bug $title build errors:
-	grep "error:" < $T
+	grep "error:" < $F
 	exit 2
 fi
-exit 0
 
-if egrep -q "rcu[^/]*\.c.*warning:|rcu.*\.h.*warning:" < $T
+grep warning: < $F > $T/warnings
+grep "include/linux/*rcu*\.h:" $T/warnings > $T/hwarnings
+grep "kernel/rcu/[^/]*:" $T/warnings > $T/cwarnings
+cat $T/hwarnings $T/cwarnings > $T/rcuwarnings
+if test -s $T/rcuwarnings
 then
 	print_warning $title build errors:
-	egrep "rcu[^/]*\.c.*warning:|rcu.*\.h.*warning:" < $T
+	cat $T/rcuwarnings
 	exit 2
 fi
 exit 0

tools/testing/selftests/rcutorture/bin/parse-console.sh

···
 then
 	print_warning Console output contains nul bytes, old qemu still running?
 fi
-egrep 'Badness|WARNING:|Warn|BUG|===========|Call Trace:|Oops:' < $file | grep -v 'ODEBUG: ' | grep -v 'Warning: unable to open an initial console' > $T
+egrep 'Badness|WARNING:|Warn|BUG|===========|Call Trace:|Oops:|Stall ended before state dump start' < $file | grep -v 'ODEBUG: ' | grep -v 'Warning: unable to open an initial console' > $T
 if test -s $T
 then
 	print_warning Assertion failure in $file $title