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

[Peter Zijlstra]

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.