linux-kernel - Re: kerneloops.org: 2.6.28-rc regression in epoll (list corruption)

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Date:	Sun, 26 Oct 2008 12:33:32 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, davidel@...ilserver.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: kerneloops.org: 2.6.28-rc regression in epoll (list corruption)

On Sun, 26 Oct 2008 11:58:06 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Sun, 26 Oct 2008, Arjan van de Ven wrote:
> >
> > This one is upcoming fast (and I just hit it as well)
> > 
> > http://www.kerneloops.org/searchweek.php?search=ep_poll_callback
> > 
> > seems epoll grew some list corruption....
> 
> It sounds very much like f337b9c58332bdecde965b436e47ea4c94d30da0
> ("epoll: drop unnecessary test") deleted a test that wasn't so
> unnecessary after all..
> 
> That ep_poll_callback() code is:
> 
>         /* If this file is already in the ready list we exit soon */
>         if (ep_is_linked(&epi->rdllink))
>                 goto is_linked;
> 
>         list_add_tail(&epi->rdllink, &ep->rdllist);
> 
> and the unnecessary test that was removed looks _very_ much like that
> kind of code.
> 
> Thomas? Davide?
> 
> And if somebody knows how to reproduce this reliably, it would be
> really good to hear if doing a revert on that thing just fixed it. It
> should revert cleanly - it's the only change to fs/eventpoll.c since
> 2.6.27.
> 

I did the revert and did the same thing I did before, and haven't seen
it yet.

(this is obviously a really small sample size on both sides of the
line, but it's at least not show it easily now while I saw it a few
times before.. after I fixed my Wifi and manually set the r8169 mac)
-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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