On Thu, Aug 06, 2015 at 02:45:43PM +0900, Hidehiro Kawai wrote:
>  void crash_kexec(struct pt_regs *regs)
>  {
> +     int old_cpu, this_cpu;
> +
> +     /*
> +      * `old_cpu == -1' means we are the first comer and crash_kexec()
> +      * was called without entering panic().
> +      * `old_cpu == this_cpu' means crash_kexec() was called from panic().
> +      */
> +     this_cpu = raw_smp_processor_id();
> +     old_cpu = atomic_cmpxchg(&panic_cpu, -1, this_cpu);
> +     if (old_cpu != -1 && old_cpu != this_cpu)
> +             return;

This allows recursive calling of crash_kexec(), the Changelog did not
mention that. Is this really required?

> +
>       /* Take the kexec_mutex here to prevent sys_kexec_load
>        * running on one cpu from replacing the crash kernel
>        * we are using after a panic on a different cpu.

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