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Re: [V3 PATCH 3/4] kexec: Fix race between panic() and crash_kexec() called directly

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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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Re: [V3 PATCH 3/4] kexec: Fix race between panic() and crash_kexec()  called directly Peter Zijlstra <peterz@infradead.org> - 2015-08-21 01:10 +0200
  RE: [V3 PATCH 3/4] kexec: Fix race between panic() and  crash_kexec() called directly 河合英宏 / KAWAI，HIDEHIRO   <hidehiro.kawai.ez@hitachi.com> - 2015-08-22 04:40 +0200
    Re: [V3 PATCH 3/4] kexec: Fix race between panic() and crash_kexec()  called directly Peter Zijlstra <peterz@infradead.org> - 2015-08-25 17:00 +0200
      RE: [V3 PATCH 3/4] kexec: Fix race between panic() and  crash_kexec() called directly 河合英宏 / KAWAI，HIDEHIRO   <hidehiro.kawai.ez@hitachi.com> - 2015-08-26 05:20 +0200
        RE: [V3 PATCH 3/4] kexec: Fix race between panic() and  crash_kexec() called directly 河合英宏 / KAWAI，HIDEHIRO   <hidehiro.kawai.ez@hitachi.com> - 2015-08-31 11:00 +0200
          Re: [V3 PATCH 3/4] kexec: Fix race between panic() and crash_kexec()  called directly Peter Zijlstra <peterz@infradead.org> - 2015-08-31 11:10 +0200
            RE: [V3 PATCH 3/4] kexec: Fix race between panic() and  crash_kexec() called directly 河合英宏 / KAWAI，HIDEHIRO   <hidehiro.kawai.ez@hitachi.com> - 2015-08-31 12:00 +0200

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