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From: Arun Sharma <asharma@fb.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Maximilian Engelhardt <maxi@daemonizer.de>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	StuStaNet Vorstand <vorstand@stusta.mhn.de>
Subject: Re: Kernel crash after using new Intel NIC (igb)
Date: Thu, 26 May 2011 12:30:04 -0700	[thread overview]
Message-ID: <4DDEAA3C.7020502@fb.com> (raw)
In-Reply-To: <1306305331.3305.22.camel@edumazet-laptop>

On 5/24/11 11:35 PM, Eric Dumazet wrote:

>> Another possibility is to do the list_empty() check twice. Once without
>> taking the lock and again with the spinlock held.
>>
>
> Why ?
>

Part of the problem is that I don't have a precise understanding of the 
race condition that's causing the list to become corrupted.

All I know is that doing it under the lock fixes it. If it's slowing 
things down, we do a check outside the lock (since it's cheap). But if 
we get the wrong answer, we verify it again under the lock.

> list_del_init(&p->unused); (done under lock of course) is safe, you can
> call it twice, no problem.

Doing it twice is not a problem. But doing it when we shouldn't be doing 
it could be the problem.

The list modification under unused_peers.lock looks generally safe. But 
the control flow (based on refcnt) done outside the lock might have races.

Eg: inet_putpeer() might find the refcnt go to zero, but before it adds 
it to the unused list, another thread may be doing inet_getpeer() and 
set refcnt to 1. In the end, we end up with a node that's potentially in 
use, but ends up on the unused list.

  -Arun

  parent reply	other threads:[~2011-05-26 19:29 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-24 22:32 Kernel crash after using new Intel NIC (igb) Maximilian Engelhardt
2011-04-26 23:34 ` Wyborny, Carolyn
2011-04-27 11:46   ` Maximilian Engelhardt
2011-04-27 12:04     ` Eric Dumazet
2011-04-27  4:24 ` Eric Dumazet
2011-04-27  4:32   ` Eric Dumazet
2011-04-27 11:51     ` Maximilian Engelhardt
2011-05-12 21:10       ` Arun Sharma
2011-05-12 21:15         ` Eric Dumazet
2011-05-24 21:33           ` Arun Sharma
2011-05-25  2:44             ` Eric Dumazet
2011-05-25  6:06               ` Arun Sharma
2011-05-25  6:35                 ` Eric Dumazet
2011-05-26 15:06                   ` Ben Hutchings
2011-05-26 19:30                   ` Arun Sharma [this message]
2011-05-26 19:47                     ` Eric Dumazet
2011-05-26 21:48                       ` Arun Sharma
2011-05-26 22:01                         ` Eric Dumazet
2011-05-27  0:09                           ` Arun Sharma
2011-05-27  3:27                             ` Eric Dumazet
2011-05-27  7:56                               ` Yann Dupont
2011-05-27 17:40                               ` David Miller
2011-05-27 17:52                               ` Arun Sharma
2011-05-27 19:56                                 ` Eric Dumazet
2011-05-27 21:14                                   ` Arun Sharma
2011-05-28  5:41                                     ` Eric Dumazet
2011-05-28 18:04                                       ` Ingo Molnar
2011-05-29  7:33                                         ` Eric Dumazet
2011-05-29  7:38                                           ` Ingo Molnar
2011-05-29  7:43                                             ` Eric Dumazet
2011-05-29 12:33                                               ` Ingo Molnar
2011-05-30 18:34                                                 ` Arun Sharma
2011-05-31 10:50                                                   ` Ingo Molnar
2011-07-13 13:38                               ` Maximilian Engelhardt

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