Re: fuse: fix hang on SMP

[Mike Day <ncmike@ncultra.org>]

On 16/10/06 16:51 -0700, Andrew Morton wrote:
> On Mon, 16 Oct 2006 18:27:10 +0200
> Miklos Szeredi <miklos@szeredi.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@us.ibm.com AIM: ncmikeday  Yahoo: ultra.runner
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