linux-kernel - Re: [patch] fix infinite loop in generic_file_splice

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Message-ID: <20080409195243.GR12774@kernel.dk>
Date:	Wed, 9 Apr 2008 21:52:44 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Allard Hoeve <allard@...e.nl>,
	Neil Brown <neilb@...e.de>
Subject: Re: [patch] fix infinite loop in generic_file_splice_read()

On Wed, Apr 09 2008, Andrew Morton wrote:
> On Wed, 09 Apr 2008 17:57:56 +0200
> Miklos Szeredi <miklos@...redi.hu> wrote:
> 
> > generic_file_splice_read() goes into an infinite loop if it races with
> > truncation.  I've found this with fsx-linux on NFS over fuse.
> > 
> > Perhaps the whole while() loop is bogus, but I can't tell from a
> > cursory glance at __generic_file_splice_read() if it will return zero
> > only on EOF, or it can do that for other reasons as well.  In the
> > latter case the loop is obviously needed.
> > 
> > This simplistic patch fixes the issue for me.
> > 
> 
> We found suspicious-looking code in generic_file_splice_read() back in
> February.  See http://lkml.org/lkml/2008/2/29/443.  I suspect that patch
> (if it works) will address the truncate lockup as well - it zaps the loop
> entirely.
> 
> Unfortunately Allard never got back to us (probably because he's running
> 2.6.24 which has a quite different generic_file_splice_read()) and the
> patch didn't get anywhere.

Hmm strange, I was pretty sure I pushed my patch back then. I'll double
check and make sure it gets upstream asap.

> Nobody has tested this at all, to my knowledge.

The original reporter did not, however others did.

-- 
Jens Axboe

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