Re: [PATCH 4.4 13/16] ocfs2: should wait dio before inode lock in ocfs2_setattr()

[Greg Kroah-Hartman]

On Wed, Dec 06, 2017 at 09:02:42AM +0800, alex chen wrote:
> Hi Ben,
> 
> Thanks for your reply.
> 
> On 2017/12/5 23:49, Ben Hutchings wrote:
> > On Wed, 2017-11-22 at 11:12 +0100, Greg Kroah-Hartman wrote:
> >> 4.4-stable review patch.  If anyone has any objections, please let me know.
> >>
> >> ------------------
> >>
> >> From: alex chen <alex.chen@xxxxxxxxxx>
> >>
> >> commit 28f5a8a7c033cbf3e32277f4cc9c6afd74f05300 upstream.
> >>
> >> we should wait dio requests to finish before inode lock in
> >> ocfs2_setattr(), otherwise the following deadlock will happen:
> > [...]
> > 
> > I looked at the kernel-doc for inode_dio_wait():
> > 
> > /**
> >  * inode_dio_wait - wait for outstanding DIO requests to finish
> >  * @inode: inode to wait for
> >  *
> >  * Waits for all pending direct I/O requests to finish so that we can
> >  * proceed with a truncate or equivalent operation.
> >  *
> >  * Must be called under a lock that serializes taking new references
> >  * to i_dio_count, usually by inode->i_mutex.
> >  */
> > 
> > Now that ocfs2_setattr() calls this outside of the inode locked region,
> > what prevents another task adding a new dio request immediately
> > afterward?
> >
> 
> In the kernel 4.6, firstly, we use the inode_lock() in do_truncate() to
> prevent another bio to be issued from this node.
> Furthermore, we use the ocfs2_rw_lock() and ocfs2_inode_lock() in ocfs2_setattr()
> to guarantee no more bio will be issued from the other nodes in this cluster.
> 
> > Also, ocfs2_dio_end_io_write() was introduced in 4.6 and it looks like
> > the dio completion path didn't previously take the inode lock.  So it
> > doesn't look this fix is needed in 3.18 or 4.4.
> 
> Yes, ocfs2_dio_end_io_write() was introduced in 4.6 and the problem this patch
> fixes is only exist in the kernel 4.6 and above 4.6.
> 
> I'm sorry that I don't clearly point out which the stable version of kernel this patch
> will fixes.

Not a problem, now dropped.

greg k-h