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

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Date:	Tue, 17 Oct 2006 08:53:50 -0400
From:	Mike Day <ncmike@...ltra.org>
To:	Andrew Morton <akpm@...l.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>, 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:

+static void fuse_vmtruncate(struct inode *inode, loff_t offset)
+{
+       struct fuse_conn *fc = get_fuse_conn(inode);
+       int need_trunc;
+
+       spin_lock(&fc->lock);
+       need_trunc = inode->i_size > offset;
+       i_size_write(inode, offset);
+       spin_unlock(&fc->lock);

-- 
Mike D. Day
IBM LTC
Cell: 919 412-3900
Sametime: ncmike@...ibm.com AIM: ncmikeday  Yahoo: ultra.runner
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