From: Chris Metcalf <cmetcalf@xxxxxxxxxxxx> Subject: nmi_backtrace: do a local dump_stack() instead of a self-NMI Currently on arm there is code that checks whether it should call dump_stack() explicitly, to avoid trying to raise an NMI when the current context is not preemptible by the backtrace IPI. Similarly, the forthcoming arch/tile support uses an IPI mechanism that does not support generating an NMI to self. Accordingly, move the code that guards this case into the generic mechanism, and invoke it unconditionally whenever we want a backtrace of the current cpu. It seems plausible that in all cases, dump_stack() will generate better information than generating a stack from the NMI handler. The register state will be missing, but that state is likely not particularly helpful in any case. Or, if we think it is helpful, we should be capturing and emitting the current register state in all cases when regs == NULL is passed to nmi_cpu_backtrace(). Link: http://lkml.kernel.org/r/1472487169-14923-3-git-send-email-cmetcalf@xxxxxxxxxxxx Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxxxx> Tested-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx> [arm] Reviewed-by: Petr Mladek <pmladek@xxxxxxxx> Acked-by: Aaron Tomlin <atomlin@xxxxxxxxxx> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/arm/kernel/smp.c | 9 --------- lib/nmi_backtrace.c | 9 +++++++++ 2 files changed, 9 insertions(+), 9 deletions(-) diff -puN arch/arm/kernel/smp.c~nmi_backtrace-do-a-local-dump_stack-instead-of-a-self-nmi arch/arm/kernel/smp.c --- a/arch/arm/kernel/smp.c~nmi_backtrace-do-a-local-dump_stack-instead-of-a-self-nmi +++ a/arch/arm/kernel/smp.c @@ -748,15 +748,6 @@ core_initcall(register_cpufreq_notifier) static void raise_nmi(cpumask_t *mask) { - /* - * Generate the backtrace directly if we are running in a calling - * context that is not preemptible by the backtrace IPI. Note - * that nmi_cpu_backtrace() automatically removes the current cpu - * from mask. - */ - if (cpumask_test_cpu(smp_processor_id(), mask) && irqs_disabled()) - nmi_cpu_backtrace(NULL); - smp_cross_call(mask, IPI_CPU_BACKTRACE); } diff -puN lib/nmi_backtrace.c~nmi_backtrace-do-a-local-dump_stack-instead-of-a-self-nmi lib/nmi_backtrace.c --- a/lib/nmi_backtrace.c~nmi_backtrace-do-a-local-dump_stack-instead-of-a-self-nmi +++ a/lib/nmi_backtrace.c @@ -49,6 +49,15 @@ void nmi_trigger_cpumask_backtrace(const if (exclude_self) cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask)); + /* + * Don't try to send an NMI to this cpu; it may work on some + * architectures, but on others it may not, and we'll get + * information at least as useful just by doing a dump_stack() here. + * Note that nmi_cpu_backtrace(NULL) will clear the cpu bit. + */ + if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask))) + nmi_cpu_backtrace(NULL); + if (!cpumask_empty(to_cpumask(backtrace_mask))) { pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n", this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask)); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
