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From: Chris Friesen <chris.friesen@windriver.com>
To: Austin Schuh <austin@peloton-tech.com>, <pavel@pavlinux.ru>
Cc: "J. Bruce Fields" <bfields@fieldses.org>,
	<linux-ext4@vger.kernel.org>, <tytso@mit.edu>,
	<adilger.kernel@dilger.ca>,
	rt-users <linux-rt-users@vger.kernel.org>
Subject: Re: RT/ext4/jbd2 circular dependency
Date: Mon, 27 Oct 2014 13:57:14 -0600	[thread overview]
Message-ID: <544EA39A.1080005@windriver.com> (raw)
In-Reply-To: <544940EF.7090907@windriver.com>

On 10/23/2014 11:54 AM, Chris Friesen wrote:

> Basically it looks like we have a circular dependency involving the
> inode->i_data_sem rt_mutex, the PG_writeback bit, and the BJ_Shadow list.  It
> goes something like this:
>
> jbd2_journal_commit_transaction:
> 1) set page for writeback (set PG_writeback bit)
> 2) put jbd2 journal head on BJ_Shadow list
> 3) sleep on PG_writeback bit waiting for page writeback complete
>
> ext4_da_writepages:
> 1) ext4_map_blocks() acquires inode->i_data_sem for writing
> 2) do_get_write_access() sleeps waiting for jbd2 journal head to come off
> the BJ_Shadow list
>
> At this point the flush code can't run because it can't acquire
> inode->i_data_sem for reading, so the page will never get written out.
> Deadlock.

Just curious...would we expect lockdep to detect this sort of thing?  I 
wasn't sure if the introduction of the two wait queues would cause 
complications.

Chris

  parent reply	other threads:[~2014-10-27 19:57 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-17 17:50 Hang writing to nfs-mounted filesystem from client, all nfsd tasks on server blocked in D Chris Friesen
2014-10-17 17:50 ` Chris Friesen
2014-10-17 18:01 ` Pavel Vasilyev
     [not found]   ` <CANGgnMbQmsdMDJUx7Bop9Xs=jQMmAJgWRjhXVFUGx-DwF=inYw@mail.gmail.com>
2014-10-23 17:54     ` RT/ext4/jbd2 circular dependency (was: Re: Hang writing to nfs-mounted filesystem from client) Chris Friesen
2014-10-26 14:25       ` Thomas Gleixner
2014-10-27 16:22         ` RT/ext4/jbd2 circular dependency Chris Friesen
2014-10-29 18:05           ` Thomas Gleixner
2014-10-29 19:11             ` Chris Friesen
2014-10-29 19:26               ` Thomas Gleixner
2014-10-29 20:17                 ` Chris Friesen
2014-10-29 20:31                   ` Thomas Gleixner
2014-10-29 23:19                 ` Theodore Ts'o
2014-10-29 23:37                   ` Chris Friesen
2014-10-30  1:44                     ` Theodore Ts'o
2014-10-30  8:15                       ` Kevin Liao
2014-10-30 12:24                         ` Theodore Ts'o
2014-10-30 21:11                   ` Thomas Gleixner
2014-10-30 23:24                     ` Theodore Ts'o
2014-10-31  0:08                       ` Chris Friesen
2014-10-31  0:16                       ` Thomas Gleixner
2014-11-13 19:06                       ` Jan Kara
2014-10-27 19:57       ` Chris Friesen [this message]
     [not found] ` <544156FE.7070905-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org>
2014-10-17 18:58   ` Hang writing to nfs-mounted filesystem from client, all nfsd tasks on server blocked in D Austin Schuh
2014-10-17 18:58     ` Austin Schuh
2014-10-17 19:12   ` Dmitry Monakhov
2014-10-17 19:12     ` Dmitry Monakhov
2014-10-18 17:05   ` Hang writing to nfs-mounted filesystem from client -- expected code path? Chris Friesen
2014-10-18 17:05     ` Chris Friesen

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