From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave Chinner <david@fromorbit.com>
Subject: Re: [RFC PATCH 2/2] Btrfs: fix deadlock on umount by umount_prepare
 interface
Date: Thu, 22 Mar 2012 17:29:02 +1100
Message-ID: <20120322062902.GF3592@dastard>
References: <4F6A98CD.5090701@cn.fujitsu.com>
 <20120322043936.GD3592@dastard>
 <4F6AB7C6.4020300@cn.fujitsu.com>
Mime-Version: 1.0
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Cc: Chris Mason <chris.mason@oracle.com>,
	viro <viro@zeniv.linux.org.uk>,
	Linux Btrfs <linux-btrfs@vger.kernel.org>,
	Linux Fsdevel <linux-fsdevel@vger.kernel.org>
To: Miao Xie <miaox@cn.fujitsu.com>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
In-Reply-To: <4F6AB7C6.4020300@cn.fujitsu.com>
List-ID: <linux-btrfs.vger.kernel.org>

On Thu, Mar 22, 2012 at 01:25:26PM +0800, Miao Xie wrote:
> On Thu, 22 Mar 2012 15:39:36 +1100, Dave Chinner wrote:
> > On Thu, Mar 22, 2012 at 11:13:17AM +0800, Miao Xie wrote:
> >> The reason the deadlock is that:
> >>   Task					Btrfs-cleaner
> >>   umount()
> >>     down_write(&s->s_umount)
> >>     close_ctree()
> >>       wait for the end of
> >>       btrfs-cleaner
> >> 					start_transaction
> >> 					  reserve space
> >> 					    shrink_delalloc()
> >> 					      writeback_inodes_sb_nr_if_idle()
> >> 						down_read(&sb->s_umount)
> >> So, the deadlock has happened.
> > 
> > Every time a deadlock involving writeback_inodes_sb...if_idle()
> > comes up, I give the same response. If the s_umount is write locked,
> > then the sb is not idle. IOWs, writeback_inodes_sb...if_idle()
> > should be doing down_read_trylock(), not down_read().
> 
> Someone did this work several months ago, but those patches have not been
> applied until now, so...

... work to get them into the current/next release.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com