linux-kernel - Re: [PATCH] deadlock when swapping to FAT

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Message-ID: <Pine.LNX.4.64.0903142153330.23664@hs20-bc2-1.build.redhat.com>
Date:	Sat, 14 Mar 2009 21:54:38 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] deadlock when swapping to FAT



On Fri, 13 Mar 2009, OGAWA Hirofumi wrote:

> Mikulas Patocka <mpatocka@...hat.com> writes:
> 
> > swapon will deadlock when an attempt to swap to a file on FAT filesystem 
> > is made. swapon holds i_mutex and FAT bmap is attempting to take it again.
> >
> > This bug was introduced somewhere between 2.6.27 and 2.6.28.
> >
> > No other filesystem is taking i_mutex in bmap, so I removed it as well.
> >
> > Note that there are many other cases where bmap can race with truncate in 
> > almost all the filesystems. They don't impose an immediate threat because 
> > bmap can be only called by root. These problems should be solved in a 
> > generic way, not in individual filesystems.
> 
> Thanks. This was fixed recently with a bit different way.
> -- 
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>

Note that the same race condition is happening in all the other 
filesystems. Maybe move that i_alloc_sem up to ->bmap method caller?

Mikulas
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