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

[Ben Hutchings]

On Wed, 2017-12-06 at 09:02 +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.ÂÂIf 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():
> > 
> > /**
> > Â* inode_dio_wait - wait for outstanding DIO requests to finish
> > Â* @inode: inode to wait for
> > Â*
> > Â* Waits for all pending direct I/O requests to finish so that we can
> > Â* proceed with a truncate or equivalent operation.
> > Â*
> > Â* Must be called under a lock that serializes taking new references
> > Â* to i_dio_count, usually by inode->i_mutex.
> > Â*/
> > 
> > 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.
[...]

Yes but there seems to be a race condition - after the call to
inode_dio_wait() and before the call to inode_lock(), another dio
request can be added.

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.