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From: Vivek Goyal <vgoyal@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: Prarit Bhargava <prarit@redhat.com>,
	Andi Kleen <ak@linux.intel.com>, Jonathan Corbet <corbet@lwn.net>,
	jbaron@akamai.com, kexec@lists.infradead.org,
	Rusty Russell <rusty@rustcorp.com.au>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	Fabian Frederick <fabf@skynet.be>,
	isimatu.yasuaki@jp.fujitsu.com, "H. Peter Anvin" <hpa@zytor.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-api@vger.kernel.org
Subject: Re: [PATCH v8] kernel, add panic_on_warn
Date: Thu, 6 Nov 2014 17:07:31 -0500	[thread overview]
Message-ID: <20141106220731.GA13590@redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1411061352440.1526@chino.kir.corp.google.com>

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?

Thanks
Vivek

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WARNING: multiple messages have this Message-ID (diff)
From: Vivek Goyal <vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Prarit Bhargava <prarit-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Andi Kleen <ak-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>,
	Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org>,
	jbaron-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org,
	kexec-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>,
	linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Fabian Frederick <fabf-AgBVmzD5pcezQB+pC5nmwQ@public.gmane.org>,
	isimatu.yasuaki-+CUm20s59erQFUHtdCDX3A@public.gmane.org,
	"H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>,
	Masami Hiramatsu
	<masami.hiramatsu.pt-FCd8Q96Dh0JBDgjK7y7TUQ@public.gmane.org>,
	Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH v8] kernel, add panic_on_warn
Date: Thu, 6 Nov 2014 17:07:31 -0500	[thread overview]
Message-ID: <20141106220731.GA13590@redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1411061352440.1526-X6Q0R45D7oAcqpCFd4KODRPsWskHk0ljAL8bYrjMMd8@public.gmane.org>

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?

Thanks
Vivek

WARNING: multiple messages have this Message-ID (diff)
From: Vivek Goyal <vgoyal@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: Prarit Bhargava <prarit@redhat.com>,
	linux-kernel@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Rusty Russell <rusty@rustcorp.com.au>,
	"H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <ak@linux.intel.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
	Fabian Frederick <fabf@skynet.be>,
	isimatu.yasuaki@jp.fujitsu.com, 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
Date: Thu, 6 Nov 2014 17:07:31 -0500	[thread overview]
Message-ID: <20141106220731.GA13590@redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1411061352440.1526@chino.kir.corp.google.com>

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?

Thanks
Vivek

  reply	other threads:[~2014-11-06 22:08 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-11-05 11:42 [PATCH v8] kernel, add panic_on_warn Prarit Bhargava
2014-11-05 11:42 ` Prarit Bhargava
2014-11-05 11:42 ` Prarit Bhargava
2014-11-05 21:59 ` David Rientjes
2014-11-05 21:59   ` David Rientjes
2014-11-05 21:59   ` David Rientjes
2014-11-06 13:10   ` Prarit Bhargava
2014-11-06 13:10     ` Prarit Bhargava
2014-11-06 13:10     ` Prarit Bhargava
2014-11-06 21:57     ` David Rientjes
2014-11-06 21:57       ` David Rientjes
2014-11-06 21:57       ` David Rientjes
2014-11-06 22:07       ` Vivek Goyal [this message]
2014-11-06 22:07         ` Vivek Goyal
2014-11-06 22:07         ` Vivek Goyal
2014-11-06 22:52         ` Prarit Bhargava
2014-11-06 22:52           ` Prarit Bhargava
2014-11-06 22:52           ` Prarit Bhargava
2014-11-07 10:15         ` David Rientjes
2014-11-07 10:15           ` David Rientjes
2014-11-07 11:05           ` Prarit Bhargava
2014-11-07 11:05             ` Prarit Bhargava
2014-11-07 11:05             ` Prarit Bhargava
2014-11-07 21:09             ` David Rientjes
2014-11-07 21:09               ` David Rientjes
2014-11-08 13:29               ` Prarit Bhargava
2014-11-08 13:29                 ` Prarit Bhargava
2014-11-08 13:29                 ` Prarit Bhargava
2014-11-06 22:51       ` Prarit Bhargava
2014-11-06 22:51         ` Prarit Bhargava
2014-11-06 22:51         ` Prarit Bhargava

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