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Date: Fri, 7 Nov 2014 02:15:46 -0800 (PST)
From: David Rientjes <rientjes@google.com>
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To: Vivek Goyal <vgoyal@redhat.com>
cc: Prarit Bhargava <prarit@redhat.com>, linux-kernel@vger.kernel.org,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
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        jbaron@akamai.com, linux-doc@vger.kernel.org,
        kexec@lists.infradead.org, linux-api@vger.kernel.org
Subject: Re: [PATCH v8] kernel, add panic_on_warn
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On Thu, 6 Nov 2014, Vivek Goyal wrote:

> On Thu, Nov 06, 2014 at 01:57:36PM -0800, David Rientjes wrote:
> 
> [..]
> > You see that doing
> > 
> > 	if (panic_on_warn) {
> > 		panic_on_warn = 0;
> > 		panic(...);
> > 	}
> > 
> > is racy, I hope.  If two threads WARN() at the same time, then there's 
> > nothing preventing a double panic() because WARN() itself is not 
> > serialized against anything.  So both the current comment and your 
> > suggested revision comment are bogus.
> 
> panic() is serialized on panic_lock. So I guess it is fine to hit WARN()
> on multiple cpus. Do you see an issue there?
> 

No issue at all, what's completely mysterious is the panic_on_warn = 0 and 
the completely bogus comment that says "prevent further WARN()s from 
panicking the system" when that's racy.  There's no need to clear 
panic_on_warn at all.