linux-kernel - Re: [PATCH] epoll: Fix spurious lockdep warnings

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Message-ID: <20110908000429.GK10700@zod.bos.redhat.com>
Date:	Wed, 7 Sep 2011 20:04:29 -0400
From:	Josh Boyer <jwboyer@...hat.com>
To:	Nelson Elhage <nelhage@...hage.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Davide Libenzi <davidel@...ilserver.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Paul Bolle <pebolle@...cali.nl>, stable@...nel.org
Subject: Re: [PATCH] epoll: Fix spurious lockdep warnings

On Tue, Aug 09, 2011 at 02:11:55PM -0400, Nelson Elhage wrote:
> epoll can acquire recursively acquire ep->mtx on multiple "struct
> eventpoll"s at once in the case where one epoll fd is monitoring
> another epoll fd. This is perfectly OK, since we're careful about the
> lock ordering, but it causes spurious lockdep warnings. Annotate the
> recursion using mutex_lock_nested, and add a comment explaining the
> nesting rules for good measure.
> 
> Recent versions of systemd are triggering this, and it can also be
> demonstrated with the following trivial test program:
> 
> --------------------8<--------------------
> 
> int main(void) {
>    int e1, e2;
>    struct epoll_event evt = {
>        .events = EPOLLIN
>    };
> 
>    e1 = epoll_create1(0);
>    e2 = epoll_create1(0);
>    epoll_ctl(e1, EPOLL_CTL_ADD, e2, &evt);
>    return 0;
> }
> --------------------8<--------------------
> 
> Cc: stable@...nel.org
> Reported-by: Paul Bolle <pebolle@...cali.nl>
> Tested-by: Paul Bolle <pebolle@...cali.nl>
> Signed-off-by: Nelson Elhage <nelhage@...hage.com>

Any progress on this heading upstream?

josh
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