linux-kernel - Re: fuse: fix hang on SMP

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Message-Id: <E1GZpDl-000134-00@dorka.pomaz.szeredi.hu>
Date:	Tue, 17 Oct 2006 15:43:05 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	ncmike@...ltra.org
CC:	akpm@...l.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: fuse: fix hang on SMP

> On 16/10/06 16:51 -0700, Andrew Morton wrote:
> >On Mon, 16 Oct 2006 18:27:10 +0200
> >Miklos Szeredi <miklos@...redi.hu> wrote:
> >
> >> Fuse didn't always call i_size_write() with i_mutex held which caused
> >> rare hangs on SMP/32bit.
> >
> >Yes, that is a bit of a trap.  I'll maintain a patch in -mm which spits a
> >warning if i_size_write() is called without i_mutex held.
> >
> 
> >+void i_size_write(struct inode *inode, loff_t i_size)
> >+{
> >+	WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex));
> 
> 
> Miklos' patch would generate this warning because he uses the spinlock
> inside struct fuse_conn to synchronize the write:

Yes, this will cause a false alarm for FUSE, but it may still be
useful to find similar bugs in other filesystems.

Miklos
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