nmi_backtrace: allow excluding an arbitrary CPU

The APIs that allow backtracing across CPUs have always had a way to
exclude the current CPU. This convenience means callers didn't need to
find a place to allocate a CPU mask just to handle the common case.

Let's extend the API to take a CPU ID to exclude instead of just a
boolean. This isn't any more complex for the API to handle and allows the
hardlockup detector to exclude a different CPU (the one it already did a
trace for) without needing to find space for a CPU mask.

Arguably, this new API also encourages safer behavior. Specifically if
the caller wants to avoid tracing the current CPU (maybe because they
already traced the current CPU) this makes it more obvious to the caller
that they need to make sure that the current CPU ID can't change.

[[e-mail]: fix trigger_allbutcpu_cpu_backtrace() stub]
Link: https://lkml.kernel.org/r/20230804065935.v4.1.Ia35521b91fc781368945161d7b28538f9996c182@changeid
Signed-off-by: Douglas Anderson <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Cc: kernel test robot <[e-mail]>
Cc: Lecopzer Chen <[e-mail]>
Cc: Petr Mladek <[e-mail]>
Cc: Pingfan Liu <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/arm/include/asm/irq.h

···
 #include <linux/cpumask.h>
 
 extern void arch_trigger_cpumask_backtrace(const cpumask_t *mask,
-					   bool exclude_self);
+					   int exclude_cpu);
 #define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
 #endif
 

arch/arm/kernel/smp.c

···
 	__ipi_send_mask(ipi_desc[IPI_CPU_BACKTRACE], mask);
 }
 
-void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
 {
-	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_nmi);
+	nmi_trigger_cpumask_backtrace(mask, exclude_cpu, raise_nmi);
 }

arch/loongarch/include/asm/irq.h

···
 #define NR_IRQS_LEGACY 16
 
 #define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
-void arch_trigger_cpumask_backtrace(const struct cpumask *mask, bool exclude_self);
+void arch_trigger_cpumask_backtrace(const struct cpumask *mask, int exclude_cpu);
 
 #define MAX_IO_PICS 2
 #define NR_IRQS	(64 + (256 * MAX_IO_PICS))

arch/loongarch/kernel/process.c

···
 	}
 }
 
-void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
 {
-	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace);
+	nmi_trigger_cpumask_backtrace(mask, exclude_cpu, raise_backtrace);
 }
 
 #ifdef CONFIG_64BIT

arch/mips/include/asm/irq.h

···
 extern int get_c0_fdc_int(void);
 
 void arch_trigger_cpumask_backtrace(const struct cpumask *mask,
-				    bool exclude_self);
+				    int exclude_cpu);
 #define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
 
 #endif /* _ASM_IRQ_H */

arch/mips/kernel/process.c

···
 	}
 }
 
-void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
 {
-	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace);
+	nmi_trigger_cpumask_backtrace(mask, exclude_cpu, raise_backtrace);
 }
 
 int mips_get_process_fp_mode(struct task_struct *task)

arch/powerpc/include/asm/irq.h

···
 
 #if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI)
 extern void arch_trigger_cpumask_backtrace(const cpumask_t *mask,
-					   bool exclude_self);
+					   int exclude_cpu);
 #define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
 #endif
 

arch/powerpc/kernel/stacktrace.c

···
 	}
 }
 
-void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
 {
-	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi);
+	nmi_trigger_cpumask_backtrace(mask, exclude_cpu, raise_backtrace_ipi);
 }
 #endif /* defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI) */

arch/powerpc/kernel/watchdog.c

···
 			__cpumask_clear_cpu(c, &wd_smp_cpus_ipi);
 		}
 	} else {
-		trigger_allbutself_cpu_backtrace();
+		trigger_allbutcpu_cpu_backtrace(cpu);
 		cpumask_clear(&wd_smp_cpus_ipi);
 	}
 
···
 		xchg(&__wd_nmi_output, 1); // see wd_lockup_ipi
 
 		if (sysctl_hardlockup_all_cpu_backtrace)
-			trigger_allbutself_cpu_backtrace();
+			trigger_allbutcpu_cpu_backtrace(cpu);
 
 		if (hardlockup_panic)
 			nmi_panic(regs, "Hard LOCKUP");

arch/sparc/include/asm/irq_64.h

···
 }
 
 void arch_trigger_cpumask_backtrace(const struct cpumask *mask,
-				    bool exclude_self);
+				    int exclude_cpu);
 #define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
 
 extern void *hardirq_stack[NR_CPUS];

arch/sparc/kernel/process_64.c

···
 	}
 }
 
-void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
 {
 	struct thread_info *tp = current_thread_info();
 	struct pt_regs *regs = get_irq_regs();
···
 
 	memset(global_cpu_snapshot, 0, sizeof(global_cpu_snapshot));
 
-	if (cpumask_test_cpu(this_cpu, mask) && !exclude_self)
+	if (cpumask_test_cpu(this_cpu, mask) && this_cpu != exclude_cpu)
 		__global_reg_self(tp, regs, this_cpu);
 
 	smp_fetch_global_regs();
···
 	for_each_cpu(cpu, mask) {
 		struct global_reg_snapshot *gp;
 
-		if (exclude_self && cpu == this_cpu)
+		if (cpu == exclude_cpu)
 			continue;
 
 		gp = &global_cpu_snapshot[cpu].reg;

arch/x86/include/asm/irq.h

···
 
 #ifdef CONFIG_X86_LOCAL_APIC
 void arch_trigger_cpumask_backtrace(const struct cpumask *mask,
-				    bool exclude_self);
+				    int exclude_cpu);
 
 #define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
 #endif

arch/x86/kernel/apic/hw_nmi.c

···
 	apic->send_IPI_mask(mask, NMI_VECTOR);
 }
 
-void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
 {
-	nmi_trigger_cpumask_backtrace(mask, exclude_self,
+	nmi_trigger_cpumask_backtrace(mask, exclude_cpu,
 				      nmi_raise_cpu_backtrace);
 }
 

include/linux/nmi.h

···
 #ifdef arch_trigger_cpumask_backtrace
 static inline bool trigger_all_cpu_backtrace(void)
 {
-	arch_trigger_cpumask_backtrace(cpu_online_mask, false);
+	arch_trigger_cpumask_backtrace(cpu_online_mask, -1);
 	return true;
 }
 
-static inline bool trigger_allbutself_cpu_backtrace(void)
+static inline bool trigger_allbutcpu_cpu_backtrace(int exclude_cpu)
 {
-	arch_trigger_cpumask_backtrace(cpu_online_mask, true);
+	arch_trigger_cpumask_backtrace(cpu_online_mask, exclude_cpu);
 	return true;
 }
 
 static inline bool trigger_cpumask_backtrace(struct cpumask *mask)
 {
-	arch_trigger_cpumask_backtrace(mask, false);
+	arch_trigger_cpumask_backtrace(mask, -1);
 	return true;
 }
 
 static inline bool trigger_single_cpu_backtrace(int cpu)
 {
-	arch_trigger_cpumask_backtrace(cpumask_of(cpu), false);
+	arch_trigger_cpumask_backtrace(cpumask_of(cpu), -1);
 	return true;
 }
 
 /* generic implementation */
 void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
-				   bool exclude_self,
+				   int exclude_cpu,
 				   void (*raise)(cpumask_t *mask));
 bool nmi_cpu_backtrace(struct pt_regs *regs);
 
···
 {
 	return false;
 }
-static inline bool trigger_allbutself_cpu_backtrace(void)
+static inline bool trigger_allbutcpu_cpu_backtrace(int exclude_cpu)
 {
 	return false;
 }

kernel/watchdog.c

···
 			dump_stack();
 
 		if (softlockup_all_cpu_backtrace) {
-			trigger_allbutself_cpu_backtrace();
+			trigger_allbutcpu_cpu_backtrace(smp_processor_id());
 			clear_bit_unlock(0, &soft_lockup_nmi_warn);
 		}
 

lib/nmi_backtrace.c

···
  * they are passed being updated as a side effect of this call.
  */
 void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
-				   bool exclude_self,
+				   int exclude_cpu,
 				   void (*raise)(cpumask_t *mask))
 {
 	int i, this_cpu = get_cpu();
···
 	}
 
 	cpumask_copy(to_cpumask(backtrace_mask), mask);
-	if (exclude_self)
-		cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
+	if (exclude_cpu != -1)
+		cpumask_clear_cpu(exclude_cpu, to_cpumask(backtrace_mask));
 
 	/*
 	 * Don't try to send an NMI to this cpu; it may work on some