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
next prev 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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