Merge tag 'rcu-next-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

Pull RCU updates from Boqun Feng:
"Documentation:
- Add broken-timing possibility to stallwarn.rst
- Improve discussion of this_cpu_ptr(), add raw_cpu_ptr()
- Document self-propagating callbacks
- Point call_srcu() to call_rcu() for detailed memory ordering
- Add CONFIG_RCU_LAZY delays to call_rcu() kernel-doc header
- Clarify RCU_LAZY and RCU_LAZY_DEFAULT_OFF help text
- Remove references to old grace-period-wait primitives

srcu:
- Introduce srcu_read_{un,}lock_fast(), which is similar to
srcu_read_{un,}lock_lite(): avoid smp_mb()s in lock and unlock
at the cost of calling synchronize_rcu() in synchronize_srcu()

Moreover, by returning the percpu offset of the counter at
srcu_read_lock_fast() time, srcu_read_unlock_fast() can avoid
extra pointer dereferencing, which makes it faster than
srcu_read_{un,}lock_lite()

srcu_read_{un,}lock_fast() are intended to replace
rcu_read_{un,}lock_trace() if possible

RCU torture:
- Add get_torture_init_jiffies() to return the start time of the test
- Add a test_boost_holdoff module parameter to allow delaying
boosting tests when building rcutorture as built-in
- Add grace period sequence number logging at the beginning and end
of failure/close-call results
- Switch to hexadecimal for the expedited grace period sequence
number in the rcu_exp_grace_period trace point
- Make cur_ops->format_gp_seqs take buffer length
- Move RCU_TORTURE_TEST_{CHK_RDR_STATE,LOG_CPU} to bool
- Complain when invalid SRCU reader_flavor is specified
- Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing, which forces SRCU
uses atomics even when percpu ops are NMI safe, and use the Kconfig
for SRCU lockdep testing

Misc:
- Split rcu_report_exp_cpu_mult() mask parameter and use for tracing
- Remove READ_ONCE() for rdp->gpwrap access in __note_gp_changes()
- Fix get_state_synchronize_rcu_full() GP-start detection
- Move RCU Tasks self-tests to core_initcall()
- Print segment lengths in show_rcu_nocb_gp_state()
- Make RCU watch ct_kernel_exit_state() warning
- Flush console log from kernel_power_off()
- rcutorture: Allow a negative value for nfakewriters
- rcu: Update TREE05.boot to test normal synchronize_rcu()
- rcu: Use _full() API to debug synchronize_rcu()

Make RCU handle PREEMPT_LAZY better:
- Fix header guard for rcu_all_qs()
- rcu: Rename PREEMPT_AUTO to PREEMPT_LAZY
- Update __cond_resched comment about RCU quiescent states
- Handle unstable rdp in rcu_read_unlock_strict()
- Handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y
- osnoise: Provide quiescent states
- Adjust rcutorture with possible PREEMPT_RCU=n && PREEMPT_COUNT=y
combination
- Limit PREEMPT_RCU configurations
- Make rcutorture senario TREE07 and senario TREE10 use
PREEMPT_LAZY=y"

* tag 'rcu-next-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (59 commits)
rcutorture: Make scenario TREE07 build CONFIG_PREEMPT_LAZY=y
rcutorture: Make scenario TREE10 build CONFIG_PREEMPT_LAZY=y
rcu: limit PREEMPT_RCU configurations
rcutorture: Update ->extendables check for lazy preemption
rcutorture: Update rcutorture_one_extend_check() for lazy preemption
osnoise: provide quiescent states
rcu: Use _full() API to debug synchronize_rcu()
rcu: Update TREE05.boot to test normal synchronize_rcu()
rcutorture: Allow a negative value for nfakewriters
Flush console log from kernel_power_off()
context_tracking: Make RCU watch ct_kernel_exit_state() warning
rcu/nocb: Print segment lengths in show_rcu_nocb_gp_state()
rcu-tasks: Move RCU Tasks self-tests to core_initcall()
rcu: Fix get_state_synchronize_rcu_full() GP-start detection
torture: Make SRCU lockdep testing use srcu_read_lock_nmisafe()
srcu: Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing
rcutorture: Complain when invalid SRCU reader_flavor is specified
rcutorture: Move RCU_TORTURE_TEST_{CHK_RDR_STATE,LOG_CPU} to bool
rcutorture: Make cur_ops->format_gp_seqs take buffer length
rcutorture: Add ftrace-compatible timestamp to GP# failure/close-call output
...

Documentation/RCU/rcubarrier.rst

···
 	was first added back in 2005.  This is because on_each_cpu()
 	disables preemption, which acted as an RCU read-side critical
 	section, thus preventing CPU 0's grace period from completing
-	until on_each_cpu() had dealt with all of the CPUs.  However,
-	with the advent of preemptible RCU, rcu_barrier() no longer
-	waited on nonpreemptible regions of code in preemptible kernels,
-	that being the job of the new rcu_barrier_sched() function.
+	until on_each_cpu() had dealt with all of the CPUs.
 
 	However, with the RCU flavor consolidation around v4.20, this
 	possibility was once again ruled out, because the consolidated

Documentation/RCU/stallwarn.rst

···
 	the ``rcu_.*timer wakeup didn't happen for`` console-log message,
 	which will include additional debugging information.
 
+-	A timer issue causes time to appear to jump forward, so that RCU
+	believes that the RCU CPU stall-warning timeout has been exceeded
+	when in fact much less time has passed.  This could be due to
+	timer hardware bugs, timer driver bugs, or even corruption of
+	the "jiffies" global variable.	These sorts of timer hardware
+	and driver bugs are not uncommon when testing new hardware.
+
 -	A low-level kernel issue that either fails to invoke one of the
 	variants of rcu_eqs_enter(true), rcu_eqs_exit(true), ct_idle_enter(),
 	ct_idle_exit(), ct_irq_enter(), or ct_irq_exit() on the one

Documentation/admin-guide/kernel-parameters.txt

···
 	rcutorture.test_boost_duration= [KNL]
 			Duration (s) of each individual boost test.
 
+	rcutorture.test_boost_holdoff= [KNL]
+			Holdoff time (s) from start of test to the start
+			of RCU priority-boost testing.	Defaults to zero,
+			that is, no holdoff.
+
 	rcutorture.test_boost_interval= [KNL]
 			Interval (s) between each boost test.
 

Documentation/core-api/this_cpu_ops.rst

···
 available. Instead, the offset of the local per cpu area is simply
 added to the per cpu offset.
 
-Note that this operation is usually used in a code segment when
-preemption has been disabled. The pointer is then used to
-access local per cpu data in a critical section. When preemption
-is re-enabled this pointer is usually no longer useful since it may
-no longer point to per cpu data of the current processor.
+Note that this operation can only be used in code segments where
+smp_processor_id() may be used, for example, where preemption has been
+disabled. The pointer is then used to access local per cpu data in a
+critical section. When preemption is re-enabled this pointer is usually
+no longer useful since it may no longer point to per cpu data of the
+current processor.
 
+The special cases where it makes sense to obtain a per-CPU pointer in
+preemptible code are addressed by raw_cpu_ptr(), but such use cases need
+to handle cases where two different CPUs are accessing the same per cpu
+variable, which might well be that of a third CPU.  These use cases are
+typically performance optimizations.  For example, SRCU implements a pair
+of counters as a pair of per-CPU variables, and rcu_read_lock_nmisafe()
+uses raw_cpu_ptr() to get a pointer to some CPU's counter, and uses
+atomic_inc_long() to handle migration between the raw_cpu_ptr() and
+the atomic_inc_long().
 
 Per cpu variables and offsets
 -----------------------------

include/linux/printk.h

···
 extern bool nbcon_device_try_acquire(struct console *con);
 extern void nbcon_device_release(struct console *con);
 void nbcon_atomic_flush_unsafe(void);
+bool pr_flush(int timeout_ms, bool reset_on_progress);
 #else
 static inline __printf(1, 0)
 int vprintk(const char *s, va_list args)
···
 
 static inline void nbcon_atomic_flush_unsafe(void)
 {
+}
+
+static inline bool pr_flush(int timeout_ms, bool reset_on_progress)
+{
+	return true;
 }
 
 #endif

include/linux/rcupdate.h

···
 
 static inline void __rcu_read_unlock(void)
 {
-	preempt_enable();
 	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
 		rcu_read_unlock_strict();
+	preempt_enable();
 }
 
 static inline int rcu_preempt_depth(void)
···
 void rcu_init(void);
 extern int rcu_scheduler_active;
 void rcu_sched_clock_irq(int user);
-
-#ifdef CONFIG_TASKS_RCU_GENERIC
-void rcu_init_tasks_generic(void);
-#else
-static inline void rcu_init_tasks_generic(void) { }
-#endif
 
 #ifdef CONFIG_RCU_STALL_COMMON
 void rcu_sysrq_start(void);
···
  * sections, invocation of the corresponding RCU callback is deferred
  * until after the all the other CPUs exit their critical sections.
  *
- * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also
- * wait for regions of code with preemption disabled, including regions of
- * code with interrupts or softirqs disabled.  In pre-v5.0 kernels, which
- * define synchronize_sched(), only code enclosed within rcu_read_lock()
- * and rcu_read_unlock() are guaranteed to be waited for.
+ * Both synchronize_rcu() and call_rcu() also wait for regions of code
+ * with preemption disabled, including regions of code with interrupts or
+ * softirqs disabled.
  *
  * Note, however, that RCU callbacks are permitted to run concurrently
  * with new RCU read-side critical sections.  One way that this can happen
···
  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
  *
  * In almost all situations, rcu_read_unlock() is immune from deadlock.
- * In recent kernels that have consolidated synchronize_sched() and
- * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity
- * also extends to the scheduler's runqueue and priority-inheritance
- * spinlocks, courtesy of the quiescent-state deferral that is carried
- * out when rcu_read_unlock() is invoked with interrupts disabled.
+ * This deadlock immunity also extends to the scheduler's runqueue
+ * and priority-inheritance spinlocks, courtesy of the quiescent-state
+ * deferral that is carried out when rcu_read_unlock() is invoked with
+ * interrupts disabled.
  *
  * See rcu_read_lock() for more information.
  */

include/linux/rcupdate_wait.h

···
 struct rcu_synchronize {
 	struct rcu_head head;
 	struct completion completion;
+
+	/* This is for debugging. */
+	struct rcu_gp_oldstate oldstate;
 };
 void wakeme_after_rcu(struct rcu_head *head);
 

include/linux/rcutree.h

···
 void rcu_end_inkernel_boot(void);
 bool rcu_inkernel_boot_has_ended(void);
 bool rcu_is_watching(void);
-#ifndef CONFIG_PREEMPTION
+#ifndef CONFIG_PREEMPT_RCU
 void rcu_all_qs(void);
 #endif
 

include/linux/srcu.h

···
 #define SRCU_READ_FLAVOR_NORMAL	0x1		// srcu_read_lock().
 #define SRCU_READ_FLAVOR_NMI	0x2		// srcu_read_lock_nmisafe().
 #define SRCU_READ_FLAVOR_LITE	0x4		// srcu_read_lock_lite().
-#define SRCU_READ_FLAVOR_ALL	0x7		// All of the above.
+#define SRCU_READ_FLAVOR_FAST	0x8		// srcu_read_lock_fast().
+#define SRCU_READ_FLAVOR_ALL   (SRCU_READ_FLAVOR_NORMAL | SRCU_READ_FLAVOR_NMI | \
+				SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST) // All of the above.
+#define SRCU_READ_FLAVOR_SLOWGP	(SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST)
+						// Flavors requiring synchronize_rcu()
+						// instead of smp_mb().
+void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
 
 #ifdef CONFIG_TINY_SRCU
 #include <linux/srcutiny.h>
···
 void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
 		void (*func)(struct rcu_head *head));
 void cleanup_srcu_struct(struct srcu_struct *ssp);
-int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
-void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
-#ifdef CONFIG_TINY_SRCU
-#define __srcu_read_lock_lite __srcu_read_lock
-#define __srcu_read_unlock_lite __srcu_read_unlock
-#else // #ifdef CONFIG_TINY_SRCU
-int __srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp);
-void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) __releases(ssp);
-#endif // #else // #ifdef CONFIG_TINY_SRCU
 void synchronize_srcu(struct srcu_struct *ssp);
 
 #define SRCU_GET_STATE_COMPLETED 0x1
···
 }
 
 /**
+ * srcu_read_lock_fast - register a new reader for an SRCU-protected structure.
+ * @ssp: srcu_struct in which to register the new reader.
+ *
+ * Enter an SRCU read-side critical section, but for a light-weight
+ * smp_mb()-free reader.  See srcu_read_lock() for more information.
+ *
+ * If srcu_read_lock_fast() is ever used on an srcu_struct structure,
+ * then none of the other flavors may be used, whether before, during,
+ * or after.  Note that grace-period auto-expediting is disabled for _fast
+ * srcu_struct structures because auto-expedited grace periods invoke
+ * synchronize_rcu_expedited(), IPIs and all.
+ *
+ * Note that srcu_read_lock_fast() can be invoked only from those contexts
+ * where RCU is watching, that is, from contexts where it would be legal
+ * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
+ */
+static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *ssp) __acquires(ssp)
+{
+	struct srcu_ctr __percpu *retval;
+
+	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
+	retval = __srcu_read_lock_fast(ssp);
+	rcu_try_lock_acquire(&ssp->dep_map);
+	return retval;
+}
+
+/**
+ * srcu_down_read_fast - register a new reader for an SRCU-protected structure.
+ * @ssp: srcu_struct in which to register the new reader.
+ *
+ * Enter a semaphore-like SRCU read-side critical section, but for
+ * a light-weight smp_mb()-free reader.  See srcu_read_lock_fast() and
+ * srcu_down_read() for more information.
+ *
+ * The same srcu_struct may be used concurrently by srcu_down_read_fast()
+ * and srcu_read_lock_fast().
+ */
+static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *ssp) __acquires(ssp)
+{
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi());
+	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
+	return __srcu_read_lock_fast(ssp);
+}
+
+/**
  * srcu_read_lock_lite - register a new reader for an SRCU-protected structure.
  * @ssp: srcu_struct in which to register the new reader.
  *
···
 {
 	int retval;
 
-	srcu_check_read_flavor_lite(ssp);
+	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_LITE);
 	retval = __srcu_read_lock_lite(ssp);
 	rcu_try_lock_acquire(&ssp->dep_map);
 	return retval;
···
  * srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler.
  *
  * Calls to srcu_down_read() may be nested, similar to the manner in
- * which calls to down_read() may be nested.
+ * which calls to down_read() may be nested.  The same srcu_struct may be
+ * used concurrently by srcu_down_read() and srcu_read_lock().
  */
 static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
 {
···
 }
 
 /**
+ * srcu_read_unlock_fast - unregister a old reader from an SRCU-protected structure.
+ * @ssp: srcu_struct in which to unregister the old reader.
+ * @scp: return value from corresponding srcu_read_lock_fast().
+ *
+ * Exit a light-weight SRCU read-side critical section.
+ */
+static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
+	__releases(ssp)
+{
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
+	srcu_lock_release(&ssp->dep_map);
+	__srcu_read_unlock_fast(ssp, scp);
+}
+
+/**
+ * srcu_up_read_fast - unregister a old reader from an SRCU-protected structure.
+ * @ssp: srcu_struct in which to unregister the old reader.
+ * @scp: return value from corresponding srcu_read_lock_fast().
+ *
+ * Exit an SRCU read-side critical section, but not necessarily from
+ * the same context as the maching srcu_down_read_fast().
+ */
+static inline void srcu_up_read_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
+	__releases(ssp)
+{
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi());
+	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
+	__srcu_read_unlock_fast(ssp, scp);
+}
+
+/**
  * srcu_read_unlock_lite - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
- * @idx: return value from corresponding srcu_read_lock().
+ * @idx: return value from corresponding srcu_read_lock_lite().
  *
  * Exit a light-weight SRCU read-side critical section.
  */
···
 /**
  * srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
- * @idx: return value from corresponding srcu_read_lock().
+ * @idx: return value from corresponding srcu_read_lock_nmisafe().
  *
  * Exit an SRCU read-side critical section, but in an NMI-safe manner.
  */

include/linux/srcutiny.h

···
 {
 	int idx;
 
-	preempt_disable();  // Needed for PREEMPT_AUTO
+	preempt_disable();  // Needed for PREEMPT_LAZY
 	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
 	WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
 	preempt_enable();
 	return idx;
 }
+
+struct srcu_ctr;
+
+static inline bool __srcu_ptr_to_ctr(struct srcu_struct *ssp, struct srcu_ctr __percpu *scpp)
+{
+	return (int)(intptr_t)(struct srcu_ctr __force __kernel *)scpp;
+}
+
+static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ssp, int idx)
+{
+	return (struct srcu_ctr __percpu *)(intptr_t)idx;
+}
+
+static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct *ssp)
+{
+	return __srcu_ctr_to_ptr(ssp, __srcu_read_lock(ssp));
+}
+
+static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
+{
+	__srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp));
+}
+
+#define __srcu_read_lock_lite __srcu_read_lock
+#define __srcu_read_unlock_lite __srcu_read_unlock
 
 static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
 {
···
 }
 
 #define srcu_check_read_flavor(ssp, read_flavor) do { } while (0)
-#define srcu_check_read_flavor_lite(ssp) do { } while (0)
+#define srcu_check_read_flavor_force(ssp, read_flavor) do { } while (0)
 
 /* Defined here to avoid size increase for non-torture kernels. */
 static inline void srcu_torture_stats_print(struct srcu_struct *ssp,

include/linux/srcutree.h

···
 struct srcu_node;
 struct srcu_struct;
 
+/* One element of the srcu_data srcu_ctrs array. */
+struct srcu_ctr {
+	atomic_long_t srcu_locks;	/* Locks per CPU. */
+	atomic_long_t srcu_unlocks;	/* Unlocks per CPU. */
+};
+
 /*
  * Per-CPU structure feeding into leaf srcu_node, similar in function
  * to rcu_node.
  */
 struct srcu_data {
 	/* Read-side state. */
-	atomic_long_t srcu_lock_count[2];	/* Locks per CPU. */
-	atomic_long_t srcu_unlock_count[2];	/* Unlocks per CPU. */
+	struct srcu_ctr srcu_ctrs[2];		/* Locks and unlocks per CPU. */
 	int srcu_reader_flavor;			/* Reader flavor for srcu_struct structure? */
 						/* Values: SRCU_READ_FLAVOR_.*  */
 
···
  * Per-SRCU-domain structure, similar in function to rcu_state.
  */
 struct srcu_struct {
-	unsigned int srcu_idx;			/* Current rdr array element. */
+	struct srcu_ctr __percpu *srcu_ctrp;
 	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
 	struct lockdep_map dep_map;
 	struct srcu_usage *srcu_sup;		/* Update-side data. */
···
 #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name)						\
 {												\
 	.sda = &pcpu_name,									\
+	.srcu_ctrp = &pcpu_name.srcu_ctrs[0],							\
 	__SRCU_STRUCT_INIT_COMMON(name, usage_name)						\
 }
 
···
 #define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
 #define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
 
+int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
 void synchronize_srcu_expedited(struct srcu_struct *ssp);
 void srcu_barrier(struct srcu_struct *ssp);
 void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf);
+
+// Converts a per-CPU pointer to an ->srcu_ctrs[] array element to that
+// element's index.
+static inline bool __srcu_ptr_to_ctr(struct srcu_struct *ssp, struct srcu_ctr __percpu *scpp)
+{
+	return scpp - &ssp->sda->srcu_ctrs[0];
+}
+
+// Converts an integer to a per-CPU pointer to the corresponding
+// ->srcu_ctrs[] array element.
+static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ssp, int idx)
+{
+	return &ssp->sda->srcu_ctrs[idx];
+}
+
+/*
+ * Counts the new reader in the appropriate per-CPU element of the
+ * srcu_struct.  Returns a pointer that must be passed to the matching
+ * srcu_read_unlock_fast().
+ *
+ * Note that both this_cpu_inc() and atomic_long_inc() are RCU read-side
+ * critical sections either because they disables interrupts, because they
+ * are a single instruction, or because they are a read-modify-write atomic
+ * operation, depending on the whims of the architecture.
+ *
+ * This means that __srcu_read_lock_fast() is not all that fast
+ * on architectures that support NMIs but do not supply NMI-safe
+ * implementations of this_cpu_inc().
+ */
+static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct *ssp)
+{
+	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
+
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_fast().");
+	if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))
+		this_cpu_inc(scp->srcu_locks.counter); /* Y */
+	else
+		atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks));  /* Z */
+	barrier(); /* Avoid leaking the critical section. */
+	return scp;
+}
+
+/*
+ * Removes the count for the old reader from the appropriate
+ * per-CPU element of the srcu_struct.  Note that this may well be a
+ * different CPU than that which was incremented by the corresponding
+ * srcu_read_lock_fast(), but it must be within the same task.
+ *
+ * Note that both this_cpu_inc() and atomic_long_inc() are RCU read-side
+ * critical sections either because they disables interrupts, because they
+ * are a single instruction, or because they are a read-modify-write atomic
+ * operation, depending on the whims of the architecture.
+ *
+ * This means that __srcu_read_unlock_fast() is not all that fast
+ * on architectures that support NMIs but do not supply NMI-safe
+ * implementations of this_cpu_inc().
+ */
+static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
+{
+	barrier();  /* Avoid leaking the critical section. */
+	if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))
+		this_cpu_inc(scp->srcu_unlocks.counter);  /* Z */
+	else
+		atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks));  /* Z */
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
+}
 
 /*
  * Counts the new reader in the appropriate per-CPU element of the
···
  */
 static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
 {
-	int idx;
+	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
 
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite().");
-	idx = READ_ONCE(ssp->srcu_idx) & 0x1;
-	this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter); /* Y */
+	this_cpu_inc(scp->srcu_locks.counter); /* Y */
 	barrier(); /* Avoid leaking the critical section. */
-	return idx;
+	return __srcu_ptr_to_ctr(ssp, scp);
 }
 
 /*
···
 static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
 {
 	barrier();  /* Avoid leaking the critical section. */
-	this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);  /* Z */
+	this_cpu_inc(__srcu_ctr_to_ptr(ssp, idx)->srcu_unlocks.counter);  /* Z */
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite().");
 }
 
 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
 
-// Record _lite() usage even for CONFIG_PROVE_RCU=n kernels.
-static inline void srcu_check_read_flavor_lite(struct srcu_struct *ssp)
+// Record reader usage even for CONFIG_PROVE_RCU=n kernels.  This is
+// needed only for flavors that require grace-period smp_mb() calls to be
+// promoted to synchronize_rcu().
+static inline void srcu_check_read_flavor_force(struct srcu_struct *ssp, int read_flavor)
 {
 	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
 
-	if (likely(READ_ONCE(sdp->srcu_reader_flavor) & SRCU_READ_FLAVOR_LITE))
+	if (likely(READ_ONCE(sdp->srcu_reader_flavor) & read_flavor))
 		return;
 
 	// Note that the cmpxchg() in __srcu_check_read_flavor() is fully ordered.
-	__srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
+	__srcu_check_read_flavor(ssp, read_flavor);
 }
 
 // Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels.

include/linux/torture.h

···
 /* Initialization and cleanup. */
 bool torture_init_begin(char *ttype, int v);
 void torture_init_end(void);
+unsigned long get_torture_init_jiffies(void);
 bool torture_cleanup_begin(void);
 void torture_cleanup_end(void);
 bool torture_must_stop(void);

include/trace/events/rcu.h

···
 		__entry->gpevent = gpevent;
 	),
 
-	TP_printk("%s %ld %s",
+	TP_printk("%s %#lx %s",
 		  __entry->rcuname, __entry->gpseq, __entry->gpevent)
 );
 

init/main.c

···
 
 	init_mm_internals();
 
-	rcu_init_tasks_generic();
 	do_pre_smp_initcalls();
 	lockup_detector_init();
 

kernel/context_tracking.c

···
  */
 static noinstr void ct_kernel_exit_state(int offset)
 {
-	int seq;
-
 	/*
 	 * CPUs seeing atomic_add_return() must see prior RCU read-side
 	 * critical sections, and we also must force ordering with the
 	 * next idle sojourn.
 	 */
 	rcu_task_trace_heavyweight_enter();  // Before CT state update!
-	seq = ct_state_inc(offset);
-	// RCU is no longer watching.  Better be in extended quiescent state!
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & CT_RCU_WATCHING));
+	// RCU is still watching.  Better not be in extended quiescent state!
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !rcu_is_watching_curr_cpu());
+	(void)ct_state_inc(offset);
+	// RCU is no longer watching.
 }
 
 /*

kernel/printk/printk.c

···
 }
 EXPORT_SYMBOL(_printk);
 
-static bool pr_flush(int timeout_ms, bool reset_on_progress);
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
 
 #else /* CONFIG_PRINTK */
···
 
 static u64 syslog_seq;
 
-static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
 
 #endif /* CONFIG_PRINTK */
···
  * Context: Process context. May sleep while acquiring console lock.
  * Return: true if all usable printers are caught up.
  */
-static bool pr_flush(int timeout_ms, bool reset_on_progress)
+bool pr_flush(int timeout_ms, bool reset_on_progress)
 {
 	return __pr_flush(NULL, timeout_ms, reset_on_progress);
 }

kernel/rcu/Kconfig

···
 
 config PREEMPT_RCU
 	bool
-	default y if PREEMPTION
+	default y if (PREEMPT || PREEMPT_RT || PREEMPT_DYNAMIC)
 	select TREE_RCU
 	help
 	  This option selects the RCU implementation that is
···
 	help
 	  This option selects the full-fledged version of SRCU.
 
+config FORCE_NEED_SRCU_NMI_SAFE
+	bool "Force selection of NEED_SRCU_NMI_SAFE"
+	depends on !TINY_SRCU
+	select NEED_SRCU_NMI_SAFE
+	default n
+	help
+	  This option forces selection of the NEED_SRCU_NMI_SAFE
+	  Kconfig option, allowing testing of srcu_read_lock_nmisafe()
+	  and srcu_read_unlock_nmisafe() on architectures (like x86)
+	  that select the ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option.
+
 config NEED_SRCU_NMI_SAFE
 	def_bool HAVE_NMI && !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && !TINY_SRCU
 
···
 
 config TASKS_RCU
 	bool
-	default NEED_TASKS_RCU && (PREEMPTION || PREEMPT_AUTO)
+	default NEED_TASKS_RCU && PREEMPTION
 	select IRQ_WORK
 
 config FORCE_TASKS_RUDE_RCU
···
 	depends on RCU_NOCB_CPU
 	default n
 	help
-	  To save power, batch RCU callbacks and flush after delay, memory
-	  pressure, or callback list growing too big.
+	  To save power, batch RCU callbacks and delay starting the
+	  corresponding grace  period for multiple seconds.  The grace
+	  period will be started after this delay, in case of memory
+	  pressure, or if the corresponding CPU's callback list grows
+	  too large.
 
-	  Requires rcu_nocbs=all to be set.
+	  These delays happen only on rcu_nocbs CPUs, that is, CPUs
+	  whose callbacks have been offloaded.
 
-	  Use rcutree.enable_rcu_lazy=0 to turn it off at boot time.
+	  Use the rcutree.enable_rcu_lazy=0 kernel-boot parameter to
+	  globally disable these delays.
 
 config RCU_LAZY_DEFAULT_OFF
 	bool "Turn RCU lazy invocation off by default"
 	depends on RCU_LAZY
 	default n
 	help
-	  Allows building the kernel with CONFIG_RCU_LAZY=y yet keep it default
-	  off. Boot time param rcutree.enable_rcu_lazy=1 can be used to switch
-	  it back on.
+	  Build the kernel with CONFIG_RCU_LAZY=y, but cause the kernel
+	  to boot with these energy-efficiency delays disabled.  Use the
+	  rcutree.enable_rcu_lazy=0 kernel-boot parameter to override
+	  the this option at boot time, thus re-enabling these delays.
 
 config RCU_DOUBLE_CHECK_CB_TIME
 	bool "RCU callback-batch backup time check"

kernel/rcu/Kconfig.debug

···
 	  Say N if you are unsure.
 
 config RCU_TORTURE_TEST_CHK_RDR_STATE
-	tristate "Check rcutorture reader state"
+	bool "Check rcutorture reader state"
 	depends on RCU_TORTURE_TEST
 	default n
 	help
···
 	  Say N if you are unsure.
 
 config RCU_TORTURE_TEST_LOG_CPU
-	tristate "Log CPU for rcutorture failures"
+	bool "Log CPU for rcutorture failures"
 	depends on RCU_TORTURE_TEST
 	default n
 	help
···
 	  less probable.
 
 	  Say Y here if you want CPU IDs logged.
+	  Say N if you are unsure.
+
+config RCU_TORTURE_TEST_LOG_GP
+	bool "Log grace-period numbers for rcutorture failures"
+	depends on RCU_TORTURE_TEST
+	default n
+	help
+	  This option causes rcutorture to decorate each entry of its
+	  log of failure/close-call rcutorture reader segments with the
+	  corresponding grace-period sequence numbers.	This information
+	  can be useful, but it does incur additional overhead, overhead
+	  that can make both failures and close calls less probable.
+
+	  Say Y here if you want grace-period sequence numbers logged.
 	  Say N if you are unsure.
 
 config RCU_REF_SCALE_TEST

kernel/rcu/rcu.h

···
 {
 	unsigned long cur_s = READ_ONCE(*sp);
 
-	return ULONG_CMP_GE(cur_s, s) || ULONG_CMP_LT(cur_s, s - (2 * RCU_SEQ_STATE_MASK + 1));
+	return ULONG_CMP_GE(cur_s, s) || ULONG_CMP_LT(cur_s, s - (3 * RCU_SEQ_STATE_MASK + 1));
 }
 
 /*
···
 #endif
 static inline void rcu_gp_set_torture_wait(int duration) { }
 #endif
+unsigned long long rcutorture_gather_gp_seqs(void);
+void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len);
 
 #ifdef CONFIG_TINY_SRCU
 
···
 static inline bool rcu_watching_zero_in_eqs(int cpu, int *vp) { return false; }
 static inline unsigned long rcu_get_gp_seq(void) { return 0; }
 static inline unsigned long rcu_exp_batches_completed(void) { return 0; }
-static inline unsigned long
-srcu_batches_completed(struct srcu_struct *sp) { return 0; }
 static inline void rcu_force_quiescent_state(void) { }
 static inline bool rcu_check_boost_fail(unsigned long gp_state, int *cpup) { return true; }
 static inline void show_rcu_gp_kthreads(void) { }
···
 bool rcu_watching_zero_in_eqs(int cpu, int *vp);
 unsigned long rcu_get_gp_seq(void);
 unsigned long rcu_exp_batches_completed(void);
-unsigned long srcu_batches_completed(struct srcu_struct *sp);
 bool rcu_check_boost_fail(unsigned long gp_state, int *cpup);
 void show_rcu_gp_kthreads(void);
 int rcu_get_gp_kthreads_prio(void);
···
 void rcu_gp_slow_register(atomic_t *rgssp);
 void rcu_gp_slow_unregister(atomic_t *rgssp);
 #endif /* #else #ifdef CONFIG_TINY_RCU */
+
+#ifdef CONFIG_TINY_SRCU
+static inline unsigned long srcu_batches_completed(struct srcu_struct *sp) { return 0; }
+#else // #ifdef CONFIG_TINY_SRCU
+unsigned long srcu_batches_completed(struct srcu_struct *sp);
+#endif // #else // #ifdef CONFIG_TINY_SRCU
 
 #ifdef CONFIG_RCU_NOCB_CPU
 void rcu_bind_current_to_nocb(void);

kernel/rcu/rcutorture.c

···
 torture_param(int, stutter, 5, "Number of seconds to run/halt test");
 torture_param(int, test_boost, 1, "Test RCU prio boost: 0=no, 1=maybe, 2=yes.");
 torture_param(int, test_boost_duration, 4, "Duration of each boost test, seconds.");
+torture_param(int, test_boost_holdoff, 0, "Holdoff time from rcutorture start, seconds.");
 torture_param(int, test_boost_interval, 7, "Interval between boost tests, seconds.");
 torture_param(int, test_nmis, 0, "End-test NMI tests, 0 to disable.");
 torture_param(bool, test_no_idle_hz, true, "Test support for tickless idle CPUs");
···
 
 static int nrealnocbers;
 static int nrealreaders;
+static int nrealfakewriters;
 static struct task_struct *writer_task;
 static struct task_struct **fakewriter_tasks;
 static struct task_struct **reader_tasks;
···
 	bool rt_preempted;
 	int rt_cpu;
 	int rt_end_cpu;
+	unsigned long long rt_gp_seq;
+	unsigned long long rt_gp_seq_end;
+	u64 rt_ts;
 };
 static int err_segs_recorded;
 static struct rt_read_seg err_segs[RCUTORTURE_RDR_MAX_SEGS];
···
 	void (*gp_slow_register)(atomic_t *rgssp);
 	void (*gp_slow_unregister)(atomic_t *rgssp);
 	bool (*reader_blocked)(void);
+	unsigned long long (*gather_gp_seqs)(void);
+	void (*format_gp_seqs)(unsigned long long seqs, char *cp, size_t len);
 	long cbflood_max;
 	int irq_capable;
 	int can_boost;
···
 	.reader_blocked		= IS_ENABLED(CONFIG_RCU_TORTURE_TEST_LOG_CPU)
 				  ? has_rcu_reader_blocked
 				  : NULL,
+	.gather_gp_seqs		= rcutorture_gather_gp_seqs,
+	.format_gp_seqs		= rcutorture_format_gp_seqs,
 	.irq_capable		= 1,
 	.can_boost		= IS_ENABLED(CONFIG_RCU_BOOST),
 	.extendables		= RCUTORTURE_MAX_EXTEND,
···
 	.sync		= synchronize_rcu_busted,
 	.exp_sync	= synchronize_rcu_busted,
 	.call		= call_rcu_busted,
+	.gather_gp_seqs	= rcutorture_gather_gp_seqs,
+	.format_gp_seqs	= rcutorture_format_gp_seqs,
 	.irq_capable	= 1,
 	.extendables	= RCUTORTURE_MAX_EXTEND,
 	.name		= "busted"
···
 static int srcu_torture_read_lock(void)
 {
 	int idx;
+	struct srcu_ctr __percpu *scp;
 	int ret = 0;
+
+	WARN_ON_ONCE(reader_flavor & ~SRCU_READ_FLAVOR_ALL);
 
 	if ((reader_flavor & SRCU_READ_FLAVOR_NORMAL) || !(reader_flavor & SRCU_READ_FLAVOR_ALL)) {
 		idx = srcu_read_lock(srcu_ctlp);
···
 		idx = srcu_read_lock_lite(srcu_ctlp);
 		WARN_ON_ONCE(idx & ~0x1);
 		ret += idx << 2;
+	}
+	if (reader_flavor & SRCU_READ_FLAVOR_FAST) {
+		scp = srcu_read_lock_fast(srcu_ctlp);
+		idx = __srcu_ptr_to_ctr(srcu_ctlp, scp);
+		WARN_ON_ONCE(idx & ~0x1);
+		ret += idx << 3;
 	}
 	return ret;
 }
···
 static void srcu_torture_read_unlock(int idx)
 {
 	WARN_ON_ONCE((reader_flavor && (idx & ~reader_flavor)) || (!reader_flavor && (idx & ~0x1)));
+	if (reader_flavor & SRCU_READ_FLAVOR_FAST)
+		srcu_read_unlock_fast(srcu_ctlp, __srcu_ctr_to_ptr(srcu_ctlp, (idx & 0x8) >> 3));
 	if (reader_flavor & SRCU_READ_FLAVOR_LITE)
 		srcu_read_unlock_lite(srcu_ctlp, (idx & 0x4) >> 2);
 	if (reader_flavor & SRCU_READ_FLAVOR_NMI)
···
 	.readunlock	= srcu_torture_read_unlock,
 	.readlock_held	= torture_srcu_read_lock_held,
 	.get_gp_seq	= srcu_torture_completed,
+	.gp_diff	= rcu_seq_diff,
 	.deferred_free	= srcu_torture_deferred_free,
 	.sync		= srcu_torture_synchronize,
 	.exp_sync	= srcu_torture_synchronize_expedited,
···
 	.readunlock	= srcu_torture_read_unlock,
 	.readlock_held	= torture_srcu_read_lock_held,
 	.get_gp_seq	= srcu_torture_completed,
+	.gp_diff	= rcu_seq_diff,
 	.deferred_free	= srcu_torture_deferred_free,
 	.sync		= srcu_torture_synchronize,
 	.exp_sync	= srcu_torture_synchronize_expedited,
···
 	unsigned long gp_state;
 	unsigned long gp_state_time;
 	unsigned long oldstarttime;
+	unsigned long booststarttime = get_torture_init_jiffies() + test_boost_holdoff * HZ;
 
-	VERBOSE_TOROUT_STRING("rcu_torture_boost started");
+	if (test_boost_holdoff <= 0 || time_after(jiffies, booststarttime)) {
+		VERBOSE_TOROUT_STRING("rcu_torture_boost started");
+	} else {
+		VERBOSE_TOROUT_STRING("rcu_torture_boost started holdoff period");
+		while (time_before(jiffies, booststarttime)) {
+			schedule_timeout_idle(HZ);
+			if (kthread_should_stop())
+				goto cleanup;
+		}
+		VERBOSE_TOROUT_STRING("rcu_torture_boost finished holdoff period");
+	}
 
 	/* Set real-time priority. */
 	sched_set_fifo_low(current);
···
 			sched_set_fifo_low(current);
 	} while (!torture_must_stop());
 
+cleanup:
 	/* Clean up and exit. */
 	while (!kthread_should_stop()) {
 		torture_shutdown_absorb("rcu_torture_boost");
···
 	do {
 		torture_hrtimeout_jiffies(torture_random(&rand) % 10, &rand);
 		if (cur_ops->cb_barrier != NULL &&
-		    torture_random(&rand) % (nfakewriters * 8) == 0) {
+		    torture_random(&rand) % (nrealfakewriters * 8) == 0) {
 			cur_ops->cb_barrier();
 		} else {
 			switch (synctype[torture_random(&rand) % nsynctypes]) {
···
 #define ROEC_ARGS "%s %s: Current %#x  To add %#x  To remove %#x  preempt_count() %#x\n", __func__, s, curstate, new, old, preempt_count()
 static void rcutorture_one_extend_check(char *s, int curstate, int new, int old, bool insoftirq)
 {
+	int mask;
+
 	if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST_CHK_RDR_STATE))
 		return;
 
···
 	WARN_ONCE(cur_ops->extendables &&
 		  !(curstate & (RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH)) &&
 		  (preempt_count() & SOFTIRQ_MASK), ROEC_ARGS);
-	WARN_ONCE(cur_ops->extendables &&
-		  !(curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED)) &&
+
+	/*
+	 * non-preemptible RCU in a preemptible kernel uses preempt_disable()
+	 * as rcu_read_lock().
+	 */
+	mask = RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
+	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
+		mask |= RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
+
+	WARN_ONCE(cur_ops->extendables && !(curstate & mask) &&
 		  (preempt_count() & PREEMPT_MASK), ROEC_ARGS);
-	WARN_ONCE(cur_ops->readlock_nesting &&
-		  !(curstate & (RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2)) &&
+
+	/*
+	 * non-preemptible RCU in a preemptible kernel uses "preempt_count() &
+	 * PREEMPT_MASK" as ->readlock_nesting().
+	 */
+	mask = RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
+	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
+		mask |= RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
+
+	WARN_ONCE(cur_ops->readlock_nesting && !(curstate & mask) &&
 		  cur_ops->readlock_nesting() > 0, ROEC_ARGS);
 }
 
···
 			if (cur_ops->reader_blocked)
 				rtrsp[-1].rt_preempted = cur_ops->reader_blocked();
 		}
+	}
+	// Sample grace-period sequence number, as good a place as any.
+	if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_LOG_GP) && cur_ops->gather_gp_seqs) {
+		rtrsp->rt_gp_seq = cur_ops->gather_gp_seqs();
+		rtrsp->rt_ts = ktime_get_mono_fast_ns();
+		if (!first)
+			rtrsp[-1].rt_gp_seq_end = rtrsp->rt_gp_seq;
 	}
 
 	/*
···
 		 "shuffle_interval=%d stutter=%d irqreader=%d "
 		 "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d "
 		 "test_boost=%d/%d test_boost_interval=%d "
-		 "test_boost_duration=%d shutdown_secs=%d "
+		 "test_boost_duration=%d test_boost_holdoff=%d shutdown_secs=%d "
 		 "stall_cpu=%d stall_cpu_holdoff=%d stall_cpu_irqsoff=%d "
 		 "stall_cpu_block=%d stall_cpu_repeat=%d "
 		 "n_barrier_cbs=%d "
···
 		 "nocbs_nthreads=%d nocbs_toggle=%d "
 		 "test_nmis=%d "
 		 "preempt_duration=%d preempt_interval=%d\n",
-		 torture_type, tag, nrealreaders, nfakewriters,
+		 torture_type, tag, nrealreaders, nrealfakewriters,
 		 stat_interval, verbose, test_no_idle_hz, shuffle_interval,
 		 stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
 		 test_boost, cur_ops->can_boost,
-		 test_boost_interval, test_boost_duration, shutdown_secs,
+		 test_boost_interval, test_boost_duration, test_boost_holdoff, shutdown_secs,
 		 stall_cpu, stall_cpu_holdoff, stall_cpu_irqsoff,
 		 stall_cpu_block, stall_cpu_repeat,
 		 n_barrier_cbs,
···
 	int flags = 0;
 	unsigned long gp_seq = 0;
 	int i;
+	int j;
 
 	if (torture_cleanup_begin()) {
 		if (cur_ops->cb_barrier != NULL) {
···
 	rcu_torture_reader_mbchk = NULL;
 
 	if (fakewriter_tasks) {
-		for (i = 0; i < nfakewriters; i++)
+		for (i = 0; i < nrealfakewriters; i++)
 			torture_stop_kthread(rcu_torture_fakewriter,
 					     fakewriter_tasks[i]);
 		kfree(fakewriter_tasks);
···
 			pr_alert("\t: No segments recorded!!!\n");
 		firsttime = 1;
 		for (i = 0; i < rt_read_nsegs; i++) {
-			pr_alert("\t%d: %#4x", i, err_segs[i].rt_readstate);
+			if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_LOG_GP))
+				pr_alert("\t%lluus ", div64_u64(err_segs[i].rt_ts, 1000ULL));
+			else
+				pr_alert("\t");
+			pr_cont("%d: %#4x", i, err_segs[i].rt_readstate);
 			if (err_segs[i].rt_delay_jiffies != 0) {
 				pr_cont("%s%ldjiffies", firsttime ? "" : "+",
 					err_segs[i].rt_delay_jiffies);
···
 					pr_cont("->%-2d", err_segs[i].rt_end_cpu);
 				else
 					pr_cont(" ...");
+			}
+			if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_LOG_GP) &&
+			    cur_ops->gather_gp_seqs && cur_ops->format_gp_seqs) {
+				char buf1[20+1];
+				char buf2[20+1];
+				char sepchar = '-';
+
+				cur_ops->format_gp_seqs(err_segs[i].rt_gp_seq,
+							buf1, ARRAY_SIZE(buf1));
+				cur_ops->format_gp_seqs(err_segs[i].rt_gp_seq_end,
+							buf2, ARRAY_SIZE(buf2));
+				if (err_segs[i].rt_gp_seq == err_segs[i].rt_gp_seq_end) {
+					if (buf2[0]) {
+						for (j = 0; buf2[j]; j++)
+							buf2[j] = '.';
+						if (j)
+							buf2[j - 1] = ' ';
+					}
+					sepchar = ' ';
+				}
+				pr_cont(" %s%c%s", buf1, sepchar, buf2);
 			}
 			if (err_segs[i].rt_delay_ms != 0) {
 				pr_cont(" %s%ldms", firsttime ? "" : "+",
···
 
 	rcu_torture_init_srcu_lockdep();
 
+	if (nfakewriters >= 0) {
+		nrealfakewriters = nfakewriters;
+	} else {
+		nrealfakewriters = num_online_cpus() - 2 - nfakewriters;
+		if (nrealfakewriters <= 0)
+			nrealfakewriters = 1;
+	}
+
 	if (nreaders >= 0) {
 		nrealreaders = nreaders;
 	} else {
···
 					  writer_task);
 	if (torture_init_error(firsterr))
 		goto unwind;
-	if (nfakewriters > 0) {
-		fakewriter_tasks = kcalloc(nfakewriters,
+
+	if (nrealfakewriters > 0) {
+		fakewriter_tasks = kcalloc(nrealfakewriters,
 					   sizeof(fakewriter_tasks[0]),
 					   GFP_KERNEL);
 		if (fakewriter_tasks == NULL) {
···
 			goto unwind;
 		}
 	}
-	for (i = 0; i < nfakewriters; i++) {
+	for (i = 0; i < nrealfakewriters; i++) {
 		firsterr = torture_create_kthread(rcu_torture_fakewriter,
 						  NULL, fakewriter_tasks[i]);
 		if (torture_init_error(firsterr))

kernel/rcu/refscale.c

···
 	.name		= "srcu"
 };
 
+static void srcu_fast_ref_scale_read_section(const int nloops)
+{
+	int i;
+	struct srcu_ctr __percpu *scp;
+
+	for (i = nloops; i >= 0; i--) {
+		scp = srcu_read_lock_fast(srcu_ctlp);
+		srcu_read_unlock_fast(srcu_ctlp, scp);
+	}
+}
+
+static void srcu_fast_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
+{
+	int i;
+	struct srcu_ctr __percpu *scp;
+
+	for (i = nloops; i >= 0; i--) {
+		scp = srcu_read_lock_fast(srcu_ctlp);
+		un_delay(udl, ndl);
+		srcu_read_unlock_fast(srcu_ctlp, scp);
+	}
+}
+
+static const struct ref_scale_ops srcu_fast_ops = {
+	.init		= rcu_sync_scale_init,
+	.readsection	= srcu_fast_ref_scale_read_section,
+	.delaysection	= srcu_fast_ref_scale_delay_section,
+	.name		= "srcu-fast"
+};
+
 static void srcu_lite_ref_scale_read_section(const int nloops)
 {
 	int i;
···
 	long i;
 	int firsterr = 0;
 	static const struct ref_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &srcu_lite_ops, RCU_TRACE_OPS RCU_TASKS_OPS
+		&rcu_ops, &srcu_ops, &srcu_fast_ops, &srcu_lite_ops, RCU_TRACE_OPS RCU_TASKS_OPS
 		&refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops,
 		&acqrel_ops, &sched_clock_ops, &clock_ops, &jiffies_ops,
 		&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,

kernel/rcu/srcutiny.c

···
 #include "rcu_segcblist.h"
 #include "rcu.h"
 
+#ifndef CONFIG_TREE_RCU
 int rcu_scheduler_active __read_mostly;
+#else // #ifndef CONFIG_TREE_RCU
+extern int rcu_scheduler_active;
+#endif // #else // #ifndef CONFIG_TREE_RCU
 static LIST_HEAD(srcu_boot_list);
 static bool srcu_init_done;
 
···
 {
 	int newval;
 
-	preempt_disable();  // Needed for PREEMPT_AUTO
+	preempt_disable();  // Needed for PREEMPT_LAZY
 	newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
 	WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
 	preempt_enable();
···
 	struct srcu_struct *ssp;
 
 	ssp = container_of(wp, struct srcu_struct, srcu_work);
-	preempt_disable();  // Needed for PREEMPT_AUTO
+	preempt_disable();  // Needed for PREEMPT_LAZY
 	if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) {
 		preempt_enable();
 		return; /* Already running or nothing to do. */
···
 	WRITE_ONCE(ssp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 	preempt_enable();
 	swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
-	preempt_disable();  // Needed for PREEMPT_AUTO
+	preempt_disable();  // Needed for PREEMPT_LAZY
 	WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
 	WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
 	preempt_enable();
···
 	 * at interrupt level, but the ->srcu_gp_running checks will
 	 * straighten that out.
 	 */
-	preempt_disable();  // Needed for PREEMPT_AUTO
+	preempt_disable();  // Needed for PREEMPT_LAZY
 	WRITE_ONCE(ssp->srcu_gp_running, false);
 	idx = ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max));
 	preempt_enable();
···
 {
 	unsigned long cookie;
 
-	preempt_disable();  // Needed for PREEMPT_AUTO
+	preempt_disable();  // Needed for PREEMPT_LAZY
 	cookie = get_state_synchronize_srcu(ssp);
 	if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) {
 		preempt_enable();
···
 
 	rhp->func = func;
 	rhp->next = NULL;
-	preempt_disable();  // Needed for PREEMPT_AUTO
+	preempt_disable();  // Needed for PREEMPT_LAZY
 	local_irq_save(flags);
 	*ssp->srcu_cb_tail = rhp;
 	ssp->srcu_cb_tail = &rhp->next;
···
 {
 	unsigned long ret;
 
-	preempt_disable();  // Needed for PREEMPT_AUTO
+	preempt_disable();  // Needed for PREEMPT_LAZY
 	ret = get_state_synchronize_srcu(ssp);
 	srcu_gp_start_if_needed(ssp);
 	preempt_enable();
···
 }
 EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
 
+#ifndef CONFIG_TREE_RCU
 /* Lockdep diagnostics.  */
 void __init rcu_scheduler_starting(void)
 {
 	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
 }
+#endif // #ifndef CONFIG_TREE_RCU
 
 /*
  * Queue work for srcu_struct structures with early boot callbacks.

kernel/rcu/srcutree.c

···
 /*
  * Initialize SRCU per-CPU data.  Note that statically allocated
  * srcu_struct structures might already have srcu_read_lock() and
- * srcu_read_unlock() running against them.  So if the is_static parameter
- * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
+ * srcu_read_unlock() running against them.  So if the is_static
+ * parameter is set, don't initialize ->srcu_ctrs[].srcu_locks and
+ * ->srcu_ctrs[].srcu_unlocks.
  */
 static void init_srcu_struct_data(struct srcu_struct *ssp)
 {
···
 	 * Initialize the per-CPU srcu_data array, which feeds into the
 	 * leaves of the srcu_node tree.
 	 */
-	BUILD_BUG_ON(ARRAY_SIZE(sdp->srcu_lock_count) !=
-		     ARRAY_SIZE(sdp->srcu_unlock_count));
 	for_each_possible_cpu(cpu) {
 		sdp = per_cpu_ptr(ssp->sda, cpu);
 		spin_lock_init(&ACCESS_PRIVATE(sdp, lock));
···
 	ssp->srcu_sup->node = NULL;
 	mutex_init(&ssp->srcu_sup->srcu_cb_mutex);
 	mutex_init(&ssp->srcu_sup->srcu_gp_mutex);
-	ssp->srcu_idx = 0;
 	ssp->srcu_sup->srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL;
 	ssp->srcu_sup->srcu_barrier_seq = 0;
 	mutex_init(&ssp->srcu_sup->srcu_barrier_mutex);
 	atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0);
 	INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu);
 	ssp->srcu_sup->sda_is_static = is_static;
-	if (!is_static)
+	if (!is_static) {
 		ssp->sda = alloc_percpu(struct srcu_data);
+		ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0];
+	}
 	if (!ssp->sda)
 		goto err_free_sup;
 	init_srcu_struct_data(ssp);
···
 }
 
 /*
- * Computes approximate total of the readers' ->srcu_lock_count[] values
- * for the rank of per-CPU counters specified by idx, and returns true if
- * the caller did the proper barrier (gp), and if the count of the locks
- * matches that of the unlocks passed in.
+ * Computes approximate total of the readers' ->srcu_ctrs[].srcu_locks
+ * values for the rank of per-CPU counters specified by idx, and returns
+ * true if the caller did the proper barrier (gp), and if the count of
+ * the locks matches that of the unlocks passed in.
  */
 static bool srcu_readers_lock_idx(struct srcu_struct *ssp, int idx, bool gp, unsigned long unlocks)
 {
···
 	for_each_possible_cpu(cpu) {
 		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
 
-		sum += atomic_long_read(&sdp->srcu_lock_count[idx]);
+		sum += atomic_long_read(&sdp->srcu_ctrs[idx].srcu_locks);
 		if (IS_ENABLED(CONFIG_PROVE_RCU))
 			mask = mask | READ_ONCE(sdp->srcu_reader_flavor);
 	}
 	WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)),
 		  "Mixed reader flavors for srcu_struct at %ps.\n", ssp);
-	if (mask & SRCU_READ_FLAVOR_LITE && !gp)
+	if (mask & SRCU_READ_FLAVOR_SLOWGP && !gp)
 		return false;
 	return sum == unlocks;
 }
 
 /*
- * Returns approximate total of the readers' ->srcu_unlock_count[] values
- * for the rank of per-CPU counters specified by idx.
+ * Returns approximate total of the readers' ->srcu_ctrs[].srcu_unlocks
+ * values for the rank of per-CPU counters specified by idx.
  */
 static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx, unsigned long *rdm)
 {
···
 	for_each_possible_cpu(cpu) {
 		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
 
-		sum += atomic_long_read(&sdp->srcu_unlock_count[idx]);
+		sum += atomic_long_read(&sdp->srcu_ctrs[idx].srcu_unlocks);
 		mask = mask | READ_ONCE(sdp->srcu_reader_flavor);
 	}
 	WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)),
···
 	unsigned long unlocks;
 
 	unlocks = srcu_readers_unlock_idx(ssp, idx, &rdm);
-	did_gp = !!(rdm & SRCU_READ_FLAVOR_LITE);
+	did_gp = !!(rdm & SRCU_READ_FLAVOR_SLOWGP);
 
 	/*
 	 * Make sure that a lock is always counted if the corresponding
···
 	 * If the locks are the same as the unlocks, then there must have
 	 * been no readers on this index at some point in this function.
 	 * But there might be more readers, as a task might have read
-	 * the current ->srcu_idx but not yet have incremented its CPU's
-	 * ->srcu_lock_count[idx] counter.  In fact, it is possible
+	 * the current ->srcu_ctrp but not yet have incremented its CPU's
+	 * ->srcu_ctrs[idx].srcu_locks counter.  In fact, it is possible
 	 * that most of the tasks have been preempted between fetching
-	 * ->srcu_idx and incrementing ->srcu_lock_count[idx].  And there
-	 * could be almost (ULONG_MAX / sizeof(struct task_struct)) tasks
-	 * in a system whose address space was fully populated with memory.
-	 * Call this quantity Nt.
+	 * ->srcu_ctrp and incrementing ->srcu_ctrs[idx].srcu_locks.  And
+	 * there could be almost (ULONG_MAX / sizeof(struct task_struct))
+	 * tasks in a system whose address space was fully populated
+	 * with memory.  Call this quantity Nt.
 	 *
-	 * So suppose that the updater is preempted at this point in the
-	 * code for a long time.  That now-preempted updater has already
-	 * flipped ->srcu_idx (possibly during the preceding grace period),
-	 * done an smp_mb() (again, possibly during the preceding grace
-	 * period), and summed up the ->srcu_unlock_count[idx] counters.
-	 * How many times can a given one of the aforementioned Nt tasks
-	 * increment the old ->srcu_idx value's ->srcu_lock_count[idx]
-	 * counter, in the absence of nesting?
+	 * So suppose that the updater is preempted at this
+	 * point in the code for a long time.  That now-preempted
+	 * updater has already flipped ->srcu_ctrp (possibly during
+	 * the preceding grace period), done an smp_mb() (again,
+	 * possibly during the preceding grace period), and summed up
+	 * the ->srcu_ctrs[idx].srcu_unlocks counters.  How many times
+	 * can a given one of the aforementioned Nt tasks increment the
+	 * old ->srcu_ctrp value's ->srcu_ctrs[idx].srcu_locks counter,
+	 * in the absence of nesting?
 	 *
 	 * It can clearly do so once, given that it has already fetched
-	 * the old value of ->srcu_idx and is just about to use that value
-	 * to index its increment of ->srcu_lock_count[idx].  But as soon as
-	 * it leaves that SRCU read-side critical section, it will increment
-	 * ->srcu_unlock_count[idx], which must follow the updater's above
-	 * read from that same value.  Thus, as soon the reading task does
-	 * an smp_mb() and a later fetch from ->srcu_idx, that task will be
-	 * guaranteed to get the new index.  Except that the increment of
-	 * ->srcu_unlock_count[idx] in __srcu_read_unlock() is after the
-	 * smp_mb(), and the fetch from ->srcu_idx in __srcu_read_lock()
-	 * is before the smp_mb().  Thus, that task might not see the new
-	 * value of ->srcu_idx until the -second- __srcu_read_lock(),
-	 * which in turn means that this task might well increment
-	 * ->srcu_lock_count[idx] for the old value of ->srcu_idx twice,
-	 * not just once.
+	 * the old value of ->srcu_ctrp and is just about to use that
+	 * value to index its increment of ->srcu_ctrs[idx].srcu_locks.
+	 * But as soon as it leaves that SRCU read-side critical section,
+	 * it will increment ->srcu_ctrs[idx].srcu_unlocks, which must
+	 * follow the updater's above read from that same value.  Thus,
+	   as soon the reading task does an smp_mb() and a later fetch from
+	 * ->srcu_ctrp, that task will be guaranteed to get the new index.
+	 * Except that the increment of ->srcu_ctrs[idx].srcu_unlocks
+	 * in __srcu_read_unlock() is after the smp_mb(), and the fetch
+	 * from ->srcu_ctrp in __srcu_read_lock() is before the smp_mb().
+	 * Thus, that task might not see the new value of ->srcu_ctrp until
+	 * the -second- __srcu_read_lock(), which in turn means that this
+	 * task might well increment ->srcu_ctrs[idx].srcu_locks for the
+	 * old value of ->srcu_ctrp twice, not just once.
 	 *
 	 * However, it is important to note that a given smp_mb() takes
 	 * effect not just for the task executing it, but also for any
 	 * later task running on that same CPU.
 	 *
-	 * That is, there can be almost Nt + Nc further increments of
-	 * ->srcu_lock_count[idx] for the old index, where Nc is the number
-	 * of CPUs.  But this is OK because the size of the task_struct
-	 * structure limits the value of Nt and current systems limit Nc
-	 * to a few thousand.
+	 * That is, there can be almost Nt + Nc further increments
+	 * of ->srcu_ctrs[idx].srcu_locks for the old index, where Nc
+	 * is the number of CPUs.  But this is OK because the size of
+	 * the task_struct structure limits the value of Nt and current
+	 * systems limit Nc to a few thousand.
 	 *
 	 * OK, but what about nesting?  This does impose a limit on
 	 * nesting of half of the size of the task_struct structure
···
 	for_each_possible_cpu(cpu) {
 		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
 
-		sum += atomic_long_read(&sdp->srcu_lock_count[0]);
-		sum += atomic_long_read(&sdp->srcu_lock_count[1]);
-		sum -= atomic_long_read(&sdp->srcu_unlock_count[0]);
-		sum -= atomic_long_read(&sdp->srcu_unlock_count[1]);
+		sum += atomic_long_read(&sdp->srcu_ctrs[0].srcu_locks);
+		sum += atomic_long_read(&sdp->srcu_ctrs[1].srcu_locks);
+		sum -= atomic_long_read(&sdp->srcu_ctrs[0].srcu_unlocks);
+		sum -= atomic_long_read(&sdp->srcu_ctrs[1].srcu_unlocks);
 	}
 	return sum;
 }
···
 	unsigned long jbase = SRCU_INTERVAL;
 	struct srcu_usage *sup = ssp->srcu_sup;
 
+	lockdep_assert_held(&ACCESS_PRIVATE(ssp->srcu_sup, lock));
 	if (srcu_gp_is_expedited(ssp))
 		jbase = 0;
 	if (rcu_seq_state(READ_ONCE(sup->srcu_gp_seq))) {
···
 void cleanup_srcu_struct(struct srcu_struct *ssp)
 {
 	int cpu;
+	unsigned long delay;
 	struct srcu_usage *sup = ssp->srcu_sup;
 
-	if (WARN_ON(!srcu_get_delay(ssp)))
+	spin_lock_irq_rcu_node(ssp->srcu_sup);
+	delay = srcu_get_delay(ssp);
+	spin_unlock_irq_rcu_node(ssp->srcu_sup);
+	if (WARN_ON(!delay))
 		return; /* Just leak it! */
 	if (WARN_ON(srcu_readers_active(ssp)))
 		return; /* Just leak it! */
···
  */
 int __srcu_read_lock(struct srcu_struct *ssp)
 {
-	int idx;
+	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
 
-	idx = READ_ONCE(ssp->srcu_idx) & 0x1;
-	this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);
+	this_cpu_inc(scp->srcu_locks.counter);
 	smp_mb(); /* B */  /* Avoid leaking the critical section. */
-	return idx;
+	return __srcu_ptr_to_ctr(ssp, scp);
 }
 EXPORT_SYMBOL_GPL(__srcu_read_lock);
 
···
 void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
 {
 	smp_mb(); /* C */  /* Avoid leaking the critical section. */
-	this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);
+	this_cpu_inc(__srcu_ctr_to_ptr(ssp, idx)->srcu_unlocks.counter);
 }
 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 
···
  */
 int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
 {
-	int idx;
-	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
+	struct srcu_ctr __percpu *scpp = READ_ONCE(ssp->srcu_ctrp);
+	struct srcu_ctr *scp = raw_cpu_ptr(scpp);
 
-	idx = READ_ONCE(ssp->srcu_idx) & 0x1;
-	atomic_long_inc(&sdp->srcu_lock_count[idx]);
+	atomic_long_inc(&scp->srcu_locks);
 	smp_mb__after_atomic(); /* B */  /* Avoid leaking the critical section. */
-	return idx;
+	return __srcu_ptr_to_ctr(ssp, scpp);
 }
 EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe);
 
···
  */
 void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 {
-	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
-
 	smp_mb__before_atomic(); /* C */  /* Avoid leaking the critical section. */
-	atomic_long_inc(&sdp->srcu_unlock_count[idx]);
+	atomic_long_inc(&raw_cpu_ptr(__srcu_ctr_to_ptr(ssp, idx))->srcu_unlocks);
 }
 EXPORT_SYMBOL_GPL(__srcu_read_unlock_nmisafe);
 
···
 /*
  * Wait until all readers counted by array index idx complete, but
  * loop an additional time if there is an expedited grace period pending.
- * The caller must ensure that ->srcu_idx is not changed while checking.
+ * The caller must ensure that ->srcu_ctrp is not changed while checking.
  */
 static bool try_check_zero(struct srcu_struct *ssp, int idx, int trycount)
 {
 	unsigned long curdelay;
 
+	spin_lock_irq_rcu_node(ssp->srcu_sup);
 	curdelay = !srcu_get_delay(ssp);
+	spin_unlock_irq_rcu_node(ssp->srcu_sup);
 
 	for (;;) {
 		if (srcu_readers_active_idx_check(ssp, idx))
···
 }
 
 /*
- * Increment the ->srcu_idx counter so that future SRCU readers will
+ * Increment the ->srcu_ctrp counter so that future SRCU readers will
  * use the other rank of the ->srcu_(un)lock_count[] arrays.  This allows
  * us to wait for pre-existing readers in a starvation-free manner.
  */
 static void srcu_flip(struct srcu_struct *ssp)
 {
 	/*
-	 * Because the flip of ->srcu_idx is executed only if the
+	 * Because the flip of ->srcu_ctrp is executed only if the
 	 * preceding call to srcu_readers_active_idx_check() found that
-	 * the ->srcu_unlock_count[] and ->srcu_lock_count[] sums matched
-	 * and because that summing uses atomic_long_read(), there is
-	 * ordering due to a control dependency between that summing and
-	 * the WRITE_ONCE() in this call to srcu_flip().  This ordering
-	 * ensures that if this updater saw a given reader's increment from
-	 * __srcu_read_lock(), that reader was using a value of ->srcu_idx
-	 * from before the previous call to srcu_flip(), which should be
-	 * quite rare.  This ordering thus helps forward progress because
-	 * the grace period could otherwise be delayed by additional
-	 * calls to __srcu_read_lock() using that old (soon to be new)
-	 * value of ->srcu_idx.
+	 * the ->srcu_ctrs[].srcu_unlocks and ->srcu_ctrs[].srcu_locks sums
+	 * matched and because that summing uses atomic_long_read(),
+	 * there is ordering due to a control dependency between that
+	 * summing and the WRITE_ONCE() in this call to srcu_flip().
+	 * This ordering ensures that if this updater saw a given reader's
+	 * increment from __srcu_read_lock(), that reader was using a value
+	 * of ->srcu_ctrp from before the previous call to srcu_flip(),
+	 * which should be quite rare.  This ordering thus helps forward
+	 * progress because the grace period could otherwise be delayed
+	 * by additional calls to __srcu_read_lock() using that old (soon
+	 * to be new) value of ->srcu_ctrp.
 	 *
 	 * This sum-equality check and ordering also ensures that if
 	 * a given call to __srcu_read_lock() uses the new value of
-	 * ->srcu_idx, this updater's earlier scans cannot have seen
+	 * ->srcu_ctrp, this updater's earlier scans cannot have seen
 	 * that reader's increments, which is all to the good, because
 	 * this grace period need not wait on that reader.  After all,
 	 * if those earlier scans had seen that reader, there would have
···
 	 */
 	smp_mb(); /* E */  /* Pairs with B and C. */
 
-	WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); // Flip the counter.
+	WRITE_ONCE(ssp->srcu_ctrp,
+		   &ssp->sda->srcu_ctrs[!(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0])]);
 
 	/*
 	 * Ensure that if the updater misses an __srcu_read_unlock()
···
 
 	check_init_srcu_struct(ssp);
 	/* If _lite() readers, don't do unsolicited expediting. */
-	if (this_cpu_read(ssp->sda->srcu_reader_flavor) & SRCU_READ_FLAVOR_LITE)
+	if (this_cpu_read(ssp->sda->srcu_reader_flavor) & SRCU_READ_FLAVOR_SLOWGP)
 		return false;
 	/* If the local srcu_data structure has callbacks, not idle.  */
 	sdp = raw_cpu_ptr(ssp->sda);
···
  * read-side critical sections are delimited by srcu_read_lock() and
  * srcu_read_unlock(), and may be nested.
  *
- * The callback will be invoked from process context, but must nevertheless
- * be fast and must not block.
+ * The callback will be invoked from process context, but with bh
+ * disabled.  The callback function must therefore be fast and must
+ * not block.
+ *
+ * See the description of call_rcu() for more detailed information on
+ * memory ordering guarantees.
  */
 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	       rcu_callback_t func)
···
  *
  * Wait for the count to drain to zero of both indexes. To avoid the
  * possible starvation of synchronize_srcu(), it waits for the count of
- * the index=((->srcu_idx & 1) ^ 1) to drain to zero at first,
- * and then flip the srcu_idx and wait for the count of the other index.
+ * the index=!(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]) to drain to zero
+ * at first, and then flip the ->srcu_ctrp and wait for the count of the
+ * other index.
  *
  * Can block; must be called from process context.
  *
···
  */
 unsigned long srcu_batches_completed(struct srcu_struct *ssp)
 {
-	return READ_ONCE(ssp->srcu_idx);
+	return READ_ONCE(ssp->srcu_sup->srcu_gp_seq);
 }
 EXPORT_SYMBOL_GPL(srcu_batches_completed);
 
···
 
 	/*
 	 * Because readers might be delayed for an extended period after
-	 * fetching ->srcu_idx for their index, at any point in time there
+	 * fetching ->srcu_ctrp for their index, at any point in time there
 	 * might well be readers using both idx=0 and idx=1.  We therefore
 	 * need to wait for readers to clear from both index values before
 	 * invoking a callback.
···
 	}
 
 	if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
-		idx = 1 ^ (ssp->srcu_idx & 1);
+		idx = !(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]);
 		if (!try_check_zero(ssp, idx, 1)) {
 			mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
 			return; /* readers present, retry later. */
···
 		 * SRCU read-side critical sections are normally short,
 		 * so check at least twice in quick succession after a flip.
 		 */
-		idx = 1 ^ (ssp->srcu_idx & 1);
+		idx = !(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]);
 		if (!try_check_zero(ssp, idx, 2)) {
 			mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
 			return; /* readers present, retry later. */
···
 	ssp = sup->srcu_ssp;
 
 	srcu_advance_state(ssp);
+	spin_lock_irq_rcu_node(ssp->srcu_sup);
 	curdelay = srcu_get_delay(ssp);
+	spin_unlock_irq_rcu_node(ssp->srcu_sup);
 	if (curdelay) {
 		WRITE_ONCE(sup->reschedule_count, 0);
 	} else {
···
 	int ss_state = READ_ONCE(ssp->srcu_sup->srcu_size_state);
 	int ss_state_idx = ss_state;
 
-	idx = ssp->srcu_idx & 0x1;
+	idx = ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0];
 	if (ss_state < 0 || ss_state >= ARRAY_SIZE(srcu_size_state_name))
 		ss_state_idx = ARRAY_SIZE(srcu_size_state_name) - 1;
 	pr_alert("%s%s Tree SRCU g%ld state %d (%s)",
···
 			struct srcu_data *sdp;
 
 			sdp = per_cpu_ptr(ssp->sda, cpu);
-			u0 = data_race(atomic_long_read(&sdp->srcu_unlock_count[!idx]));
-			u1 = data_race(atomic_long_read(&sdp->srcu_unlock_count[idx]));
+			u0 = data_race(atomic_long_read(&sdp->srcu_ctrs[!idx].srcu_unlocks));
+			u1 = data_race(atomic_long_read(&sdp->srcu_ctrs[idx].srcu_unlocks));
 
 			/*
 			 * Make sure that a lock is always counted if the corresponding
···
 			 */
 			smp_rmb();
 
-			l0 = data_race(atomic_long_read(&sdp->srcu_lock_count[!idx]));
-			l1 = data_race(atomic_long_read(&sdp->srcu_lock_count[idx]));
+			l0 = data_race(atomic_long_read(&sdp->srcu_ctrs[!idx].srcu_locks));
+			l1 = data_race(atomic_long_read(&sdp->srcu_ctrs[idx].srcu_locks));
 
 			c0 = l0 - u0;
 			c1 = l1 - u1;
···
 		ssp->sda = alloc_percpu(struct srcu_data);
 		if (WARN_ON_ONCE(!ssp->sda))
 			return -ENOMEM;
+		ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0];
 	}
 	return 0;
 }

kernel/rcu/tasks.h

···
 #endif
 }
 
-void __init rcu_init_tasks_generic(void)
+static int __init rcu_init_tasks_generic(void)
 {
 #ifdef CONFIG_TASKS_RCU
 	rcu_spawn_tasks_kthread();
···
 
 	// Run the self-tests.
 	rcu_tasks_initiate_self_tests();
+
+	return 0;
 }
+core_initcall(rcu_init_tasks_generic);
 
 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
 static inline void rcu_tasks_bootup_oddness(void) {}

kernel/rcu/tiny.c

···
 }
 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
 
+#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST)
+unsigned long long rcutorture_gather_gp_seqs(void)
+{
+	return READ_ONCE(rcu_ctrlblk.gp_seq) & 0xffffULL;
+}
+EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs);
+
+void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len)
+{
+	snprintf(cp, len, "g%04llx", seqs & 0xffffULL);
+}
+EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs);
+#endif
+
 void __init rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);

kernel/rcu/tree.c

···
 }
 EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
 
+/* Gather grace-period sequence numbers for rcutorture diagnostics. */
+unsigned long long rcutorture_gather_gp_seqs(void)
+{
+	return ((READ_ONCE(rcu_state.gp_seq) & 0xffffULL) << 40) |
+	       ((READ_ONCE(rcu_state.expedited_sequence) & 0xffffffULL) << 16) |
+	       (READ_ONCE(rcu_state.gp_seq_polled) & 0xffffULL);
+}
+EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs);
+
+/* Format grace-period sequence numbers for rcutorture diagnostics. */
+void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len)
+{
+	unsigned int egp = (seqs >> 16) & 0xffffffULL;
+	unsigned int ggp = (seqs >> 40) & 0xffffULL;
+	unsigned int pgp = seqs & 0xffffULL;
+
+	snprintf(cp, len, "g%04x:e%06x:p%04x", ggp, egp, pgp);
+}
+EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs);
+
 #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
 /*
  * An empty function that will trigger a reschedule on
···
 
 	/* Handle the ends of any preceding grace periods first. */
 	if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
-	    unlikely(READ_ONCE(rdp->gpwrap))) {
+	    unlikely(rdp->gpwrap)) {
 		if (!offloaded)
 			ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
 		rdp->core_needs_qs = false;
···
 
 	/* Now handle the beginnings of any new-to-this-CPU grace periods. */
 	if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
-	    unlikely(READ_ONCE(rdp->gpwrap))) {
+	    unlikely(rdp->gpwrap)) {
 		/*
 		 * If the current grace period is waiting for this CPU,
 		 * set up to detect a quiescent state, otherwise don't
···
 	rdp->gp_seq = rnp->gp_seq;  /* Remember new grace-period state. */
 	if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
 		WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
-	if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
+	if (IS_ENABLED(CONFIG_PROVE_RCU) && rdp->gpwrap)
 		WRITE_ONCE(rdp->last_sched_clock, jiffies);
 	WRITE_ONCE(rdp->gpwrap, false);
 	rcu_gpnum_ovf(rnp, rdp);
···
 {
 	struct rcu_synchronize *rs = container_of(
 		(struct rcu_head *) node, struct rcu_synchronize, head);
-	unsigned long oldstate = (unsigned long) rs->head.func;
 
 	WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) &&
-		!poll_state_synchronize_rcu(oldstate),
-		"A full grace period is not passed yet: %lu",
-		rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
+		!poll_state_synchronize_rcu_full(&rs->oldstate),
+		"A full grace period is not passed yet!\n");
 
 	/* Finally. */
 	complete(&rs->completion);
···
 
 	/* Advance to a new grace period and initialize state. */
 	record_gp_stall_check_time();
+	/*
+	 * A new wait segment must be started before gp_seq advanced, so
+	 * that previous gp waiters won't observe the new gp_seq.
+	 */
+	start_new_poll = rcu_sr_normal_gp_init();
 	/* Record GP times before starting GP, hence rcu_seq_start(). */
 	rcu_seq_start(&rcu_state.gp_seq);
 	ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
-	start_new_poll = rcu_sr_normal_gp_init();
 	trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
 	rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);
 	raw_spin_unlock_irq_rcu_node(rnp);
···
  * critical sections have completed.
  *
  * Use this API instead of call_rcu() if you don't want the callback to be
- * invoked after very long periods of time, which can happen on systems without
+ * delayed for very long periods of time, which can happen on systems without
  * memory pressure and on systems which are lightly loaded or mostly idle.
  * This function will cause callbacks to be invoked sooner than later at the
  * expense of extra power. Other than that, this function is identical to, and
···
  * might well execute concurrently with RCU read-side critical sections
  * that started after call_rcu() was invoked.
  *
+ * It is perfectly legal to repost an RCU callback, potentially with
+ * a different callback function, from within its callback function.
+ * The specified function will be invoked after another full grace period
+ * has elapsed.  This use case is similar in form to the common practice
+ * of reposting a timer from within its own handler.
+ *
  * RCU read-side critical sections are delimited by rcu_read_lock()
  * and rcu_read_unlock(), and may be nested.  In addition, but only in
  * v5.0 and later, regions of code across which interrupts, preemption,
···
  *
  * Implementation of these memory-ordering guarantees is described here:
  * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
+ *
+ * Specific to call_rcu() (as opposed to the other call_rcu*() functions),
+ * in kernels built with CONFIG_RCU_LAZY=y, call_rcu() might delay for many
+ * seconds before starting the grace period needed by the corresponding
+ * callback.  This delay can significantly improve energy-efficiency
+ * on low-utilization battery-powered devices.  To avoid this delay,
+ * in latency-sensitive kernel code, use call_rcu_hurry().
  */
 void call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
···
 	 * snapshot before adding a request.
 	 */
 	if (IS_ENABLED(CONFIG_PROVE_RCU))
-		rs.head.func = (void *) get_state_synchronize_rcu();
+		get_state_synchronize_rcu_full(&rs.oldstate);
 
 	rcu_sr_normal_add_req(&rs);
 
···
  */
 void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
 {
-	struct rcu_node *rnp = rcu_get_root();
-
 	/*
 	 * Any prior manipulation of RCU-protected data must happen
 	 * before the loads from ->gp_seq and ->expedited_sequence.
 	 */
 	smp_mb();  /* ^^^ */
-	rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq);
+
+	// Yes, rcu_state.gp_seq, not rnp_root->gp_seq, the latter's use
+	// in poll_state_synchronize_rcu_full() notwithstanding.  Use of
+	// the latter here would result in too-short grace periods due to
+	// interactions with newly onlined CPUs.
+	rgosp->rgos_norm = rcu_seq_snap(&rcu_state.gp_seq);
 	rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence);
 }
 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full);

kernel/rcu/tree_exp.h

···
  * specified leaf rcu_node structure, which is acquired by the caller.
  */
 static void rcu_report_exp_cpu_mult(struct rcu_node *rnp, unsigned long flags,
-				    unsigned long mask, bool wake)
+				    unsigned long mask_in, bool wake)
 				    __releases(rnp->lock)
 {
 	int cpu;
+	unsigned long mask;
 	struct rcu_data *rdp;
 
 	raw_lockdep_assert_held_rcu_node(rnp);
-	if (!(rnp->expmask & mask)) {
+	if (!(rnp->expmask & mask_in)) {
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		return;
 	}
+	mask = mask_in & rnp->expmask;
 	WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
 	for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
 		rdp = per_cpu_ptr(&rcu_data, cpu);

kernel/rcu/tree_nocb.h

···
 /* Dump out nocb kthread state for the specified rcu_data structure. */
 static void show_rcu_nocb_state(struct rcu_data *rdp)
 {
-	char bufw[20];
-	char bufr[20];
+	char bufd[22];
+	char bufw[45];
+	char bufr[45];
+	char bufn[22];
+	char bufb[22];
 	struct rcu_data *nocb_next_rdp;
 	struct rcu_segcblist *rsclp = &rdp->cblist;
 	bool waslocked;
···
 					      typeof(*rdp),
 					      nocb_entry_rdp);
 
-	sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]);
-	sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]);
-	pr_info("   CB %d^%d->%d %c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n",
+	sprintf(bufd, "%ld", rsclp->seglen[RCU_DONE_TAIL]);
+	sprintf(bufw, "%ld(%ld)", rsclp->seglen[RCU_WAIT_TAIL], rsclp->gp_seq[RCU_WAIT_TAIL]);
+	sprintf(bufr, "%ld(%ld)", rsclp->seglen[RCU_NEXT_READY_TAIL],
+		      rsclp->gp_seq[RCU_NEXT_READY_TAIL]);
+	sprintf(bufn, "%ld", rsclp->seglen[RCU_NEXT_TAIL]);
+	sprintf(bufb, "%ld", rcu_cblist_n_cbs(&rdp->nocb_bypass));
+	pr_info("   CB %d^%d->%d %c%c%c%c%c F%ld L%ld C%d %c%s%c%s%c%s%c%s%c%s q%ld %c CPU %d%s\n",
 		rdp->cpu, rdp->nocb_gp_rdp->cpu,
 		nocb_next_rdp ? nocb_next_rdp->cpu : -1,
 		"kK"[!!rdp->nocb_cb_kthread],
···
 		jiffies - rdp->nocb_nobypass_last,
 		rdp->nocb_nobypass_count,
 		".D"[rcu_segcblist_ready_cbs(rsclp)],
+		rcu_segcblist_segempty(rsclp, RCU_DONE_TAIL) ? "" : bufd,
 		".W"[!rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL)],
 		rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL) ? "" : bufw,
 		".R"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL)],
 		rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL) ? "" : bufr,
 		".N"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL)],
+		rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL) ? "" : bufn,
 		".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
+		!rcu_cblist_n_cbs(&rdp->nocb_bypass) ? "" : bufb,
 		rcu_segcblist_n_cbs(&rdp->cblist),
 		rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.',
 		rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_cb_kthread) : -1,

kernel/rcu/tree_plugin.h

···
 {
 	struct rcu_data *rdp;
 
-	if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
+	if (irqs_disabled() || in_atomic_preempt_off() || !rcu_state.gp_kthread)
 		return;
+
+	/*
+	 * rcu_report_qs_rdp() can only be invoked with a stable rdp and
+	 * from the local CPU.
+	 *
+	 * The in_atomic_preempt_off() check ensures that we come here holding
+	 * the last preempt_count (which will get dropped once we return to
+	 * __rcu_read_unlock().
+	 */
 	rdp = this_cpu_ptr(&rcu_data);
 	rdp->cpu_no_qs.b.norm = false;
 	rcu_report_qs_rdp(rdp);
···
  */
 static void rcu_flavor_sched_clock_irq(int user)
 {
-	if (user || rcu_is_cpu_rrupt_from_idle()) {
+	if (user || rcu_is_cpu_rrupt_from_idle() ||
+	     (IS_ENABLED(CONFIG_PREEMPT_COUNT) &&
+	      (preempt_count() == HARDIRQ_OFFSET))) {
 
 		/*
 		 * Get here if this CPU took its interrupt from user
-		 * mode or from the idle loop, and if this is not a
-		 * nested interrupt.  In this case, the CPU is in
-		 * a quiescent state, so note it.
+		 * mode, from the idle loop without this being a nested
+		 * interrupt, or while not holding the task preempt count
+		 * (with PREEMPT_COUNT=y). In this case, the CPU is in a
+		 * quiescent state, so note it.
 		 *
 		 * No memory barrier is required here because rcu_qs()
 		 * references only CPU-local variables that other CPUs

kernel/reboot.c

···
 	migrate_to_reboot_cpu();
 	syscore_shutdown();
 	pr_emerg("Power down\n");
+	pr_flush(1000, true);
 	kmsg_dump(KMSG_DUMP_SHUTDOWN);
 	machine_power_off();
 }

kernel/sched/core.c

···
 		return 1;
 	}
 	/*
-	 * In preemptible kernels, ->rcu_read_lock_nesting tells the tick
+	 * In PREEMPT_RCU kernels, ->rcu_read_lock_nesting tells the tick
 	 * whether the current CPU is in an RCU read-side critical section,
 	 * so the tick can report quiescent states even for CPUs looping
 	 * in kernel context.  In contrast, in non-preemptible kernels,
···
 	 * RCU quiescent state.  Therefore, the following code causes
 	 * cond_resched() to report a quiescent state, but only when RCU
 	 * is in urgent need of one.
+	 * A third case, preemptible, but non-PREEMPT_RCU provides for
+	 * urgently needed quiescent states via rcu_flavor_sched_clock_irq().
 	 */
 #ifndef CONFIG_PREEMPT_RCU
 	rcu_all_qs();

kernel/torture.c

···
 	stutter_task = NULL;
 }
 
+static unsigned long torture_init_jiffies;
+
 static void
 torture_print_module_parms(void)
 {
···
 	torture_type = ttype;
 	verbose = v;
 	fullstop = FULLSTOP_DONTSTOP;
+	WRITE_ONCE(torture_init_jiffies, jiffies); // Lockless reads.
 	torture_print_module_parms();
 	return true;
 }
···
 	register_reboot_notifier(&torture_shutdown_nb);
 }
 EXPORT_SYMBOL_GPL(torture_init_end);
+
+/*
+ * Get the torture_init_begin()-time value of the jiffies counter.
+ */
+unsigned long get_torture_init_jiffies(void)
+{
+	return READ_ONCE(torture_init_jiffies);
+}
+EXPORT_SYMBOL_GPL(get_torture_init_jiffies);
 
 /*
  * Clean up torture module.  Please note that this is -not- invoked via

kernel/trace/trace_osnoise.c

···
 
 		/*
 		 * In some cases, notably when running on a nohz_full CPU with
-		 * a stopped tick PREEMPT_RCU has no way to account for QSs.
-		 * This will eventually cause unwarranted noise as PREEMPT_RCU
-		 * will force preemption as the means of ending the current
-		 * grace period. We avoid this problem by calling
-		 * rcu_momentary_eqs(), which performs a zero duration
-		 * EQS allowing PREEMPT_RCU to end the current grace period.
-		 * This call shouldn't be wrapped inside an RCU critical
-		 * section.
+		 * a stopped tick PREEMPT_RCU or PREEMPT_LAZY have no way to
+		 * account for QSs. This will eventually cause unwarranted
+		 * noise as RCU forces preemption as the means of ending the
+		 * current grace period.  We avoid this by calling
+		 * rcu_momentary_eqs(), which performs a zero duration EQS
+		 * allowing RCU to end the current grace period. This call
+		 * shouldn't be wrapped inside an RCU critical section.
 		 *
-		 * Note that in non PREEMPT_RCU kernels QSs are handled through
-		 * cond_resched()
+		 * Normally QSs for other cases are handled through cond_resched().
+		 * For simplicity, however, we call rcu_momentary_eqs() for all
+		 * configurations here.
 		 */
-		if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
-			if (!disable_irq)
-				local_irq_disable();
+		if (!disable_irq)
+			local_irq_disable();
 
-			rcu_momentary_eqs();
+		rcu_momentary_eqs();
 
-			if (!disable_irq)
-				local_irq_enable();
-		}
+		if (!disable_irq)
+			local_irq_enable();
 
 		/*
 		 * For the non-preemptive kernel config: let threads runs, if

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

···
 		do
 			err=
 			val=$((d*1000+t*10+c))
-			tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 5s --configs "SRCU-P" --bootargs "rcutorture.test_srcu_lockdep=$val" --trust-make --datestamp "$ds/$val" > "$T/kvm.sh.out" 2>&1
+			tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 5s --configs "SRCU-P" --kconfig "CONFIG_FORCE_NEED_SRCU_NMI_SAFE=y" --bootargs "rcutorture.test_srcu_lockdep=$val rcutorture.reader_flavor=0x2" --trust-make --datestamp "$ds/$val" > "$T/kvm.sh.out" 2>&1
 			ret=$?
 			mv "$T/kvm.sh.out" "$RCUTORTURE/res/$ds/$val"
 			if test "$d" -ne 0 && test "$ret" -eq 0

tools/testing/selftests/rcutorture/configs/rcu/SRCU-P.boot

···
 rcupdate.rcu_self_test=1
 rcutorture.fwd_progress=3
 srcutree.big_cpu_lim=5
+rcutorture.reader_flavor=0x8

tools/testing/selftests/rcutorture/configs/rcu/TREE05.boot

···
 rcutree.gp_init_delay=3
 rcutree.gp_cleanup_delay=3
 rcupdate.rcu_self_test=1
+
+# This part is for synchronize_rcu() testing
+rcutorture.nfakewriters=-1
+rcutorture.gp_sync=1
+rcupdate.rcu_normal=1
+rcutree.rcu_normal_wake_from_gp=1

tools/testing/selftests/rcutorture/configs/rcu/TREE07

···
 CONFIG_SMP=y
 CONFIG_NR_CPUS=16
-CONFIG_PREEMPT_NONE=y
+CONFIG_PREEMPT_NONE=n
 CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT_LAZY=y
 CONFIG_PREEMPT=n
 CONFIG_PREEMPT_DYNAMIC=n
 #CHECK#CONFIG_TREE_RCU=y

tools/testing/selftests/rcutorture/configs/rcu/TREE10

···
 CONFIG_SMP=y
 CONFIG_NR_CPUS=74
-CONFIG_PREEMPT_NONE=y
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_LAZY=y
 CONFIG_PREEMPT_VOLUNTARY=n
 CONFIG_PREEMPT=n
 CONFIG_PREEMPT_DYNAMIC=n