linux-ext4 - Re: [Bug 13232] ext3/4 with synchronous writes gets wedged by Postfix

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Date:	Mon, 18 May 2009 14:45:20 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Tso <tytso@....edu>
Cc:	bugzilla-daemon@...zilla.kernel.org, linux-ext4@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [Bug 13232] ext3/4 with synchronous writes gets wedged by
	Postfix

On Wed 13-05-09 12:07:24, Theodore Tso wrote:
> On Wed, May 13, 2009 at 03:48:02PM +0200, Jan Kara wrote:
> >   OK, the deadlock has been introduced by ext3 variant of
> > 261bca86ed4f7f391d1938167624e78da61dcc6b (adding Al to CC).
> 
> What do you mean by this?
> 
> I'm puzzled why we haven't hit this before.  This looks like
> long-standing issue; what unmasked it now?
  Unless you mount the fs with 'sync' option, hitting this is much harder
(the window is quite small in nosync case). I think that is the main reason
why we didn't see this earlier.

> > The deadlock
> > is really tough to avoid - we have to first allocate inode on disk so
> > that we know the inode number.
> 
> Well, the simple thing to do is to have a way of quickly determining
> that a particular inode number is in the I_FREEING state, and simply
> try to avoid using that inode number.  If there are no inodes
> available, it can simply close the handle (since nothing else has
> changed at that point), wait for the current transaction to close, and
> then try again.  That should fix the problem, I think.
  Yes, we could work-around it like that but other filesystems might need
similar things and generally it would be nicer if we could avoid using this
vfs-internal information in the filesystems. Al seems to have found some
other solution without changing filesystems so that would be easier for us...

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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