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

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [V3 PATCH 3/4] kexec: Fix race between panic() and crash_kexec() called directly
Date	2015-08-31 11:10 +0200
Message-ID	<q3tge-3d0-31@gated-at.bofh.it> (permalink)
References	(2 earlier) <pZH85-2wb-7@gated-at.bofh.it> <q06SR-5HX-3@gated-at.bofh.it> <q1nRE-1aY-9@gated-at.bofh.it> <q1zpM-1JJ-9@gated-at.bofh.it> <q3t6y-2Mk-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Aug 31, 2015 at 08:53:11AM +0000, 河合英宏 / KAWAI，HIDEHIRO wrote:
> > I understand your question.  I don't intend to permit the recursive
> > call of crash_kexec() as for 'old_cpu != this_cpu' check.  That is
> > needed for the case of panic() --> crash_kexec().  Since panic_cpu has
> > already been set to this_cpu in panic() (please see PATCH 1/4), no one
> > can run crash_kexec() without 'old_cpu != this_cpu' check.
> > 
> > If you don't like this check, I would also be able to handle this case
> > like below:
> > 
> > crash_kexec()
> > {
> > 	old_cpu = atomic_cmpxchg(&panic_cpu, -1, this_cpu);
> > 	if (old_cpu != -1)
> > 		return;
> > 
> > 	__crash_kexec();
> > }
> > 
> > panic()
> > {
> > 	atomic_cmpxchg(&panic_cpu, -1, this_cpu);
> > 	__crash_kexec();
> > ...
> > 
> 
> Is that OK?

I suppose so, but I think me getting confused means comments can be
added/improved.
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Thread

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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