linux-kernel - Re: [PATCH v8] kernel, add panic_on

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Message-ID: <alpine.DEB.2.10.1411070214220.32405@chino.kir.corp.google.com>
Date:	Fri, 7 Nov 2014 02:15:46 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Vivek Goyal <vgoyal@...hat.com>
cc:	Prarit Bhargava <prarit@...hat.com>, linux-kernel@...r.kernel.org,
	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Fabian Frederick <fabf@...net.be>,
	isimatu.yasuaki@...fujitsu.com, jbaron@...mai.com,
	linux-doc@...r.kernel.org, kexec@...ts.infradead.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v8] kernel, add panic_on_warn

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.
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