linux-kernel - Re: nfs: infinite loop in fcntl(F

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Message-Id: <E1JkxKz-0003A8-9V@pomaz-ex.szeredi.hu>
Date:	Sun, 13 Apr 2008 10:13:21 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	bfields@...ldses.org
CC:	miklos@...redi.hu, trond.myklebust@....uio.no,
	eshel@...aden.ibm.com, neilb@...e.de, akpm@...ux-foundation.org,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: nfs: infinite loop in fcntl(F_SETLKW)

> > > > OK. So the correct fix here should really be applied to fcntl_setlk().
> > > > There is absolutely no reason why we should be looping at all if the
> > > > filesystem has a ->lock() method.
> > > > 
> > > > In fact, this looping behaviour was introduced recently in commit
> > > > 7723ec9777d9832849b76475b1a21a2872a40d20.
> > > 
> > > Apologies, that was indeed a behavioral change introduced in a commit
> > > that claimed just to be shuffling code around.
> > 
> > Yeah, that patch looks totally wrong.  It's not generally a good idea
> > to do a loop where the exit condition depends on something you don't
> > control.  And error values from filesystem methods are typically like
> > that.  For example with fuse, the error code could come from an
> > unprivileged userspace process.
> > 
> > I didn't realize this aspect of the bug previously, because I
> > concentrated on the lockd inconsistency.
> 
> So, does this patch on its own fix the problem you saw?

Yes.  With the patch applied, the test program returns "lockf:
Resource temporarily unavailable" instead of hanging.

Thanks,
Miklos
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