linux-kernel - Re: [PATCH RT] fs: jbd2: pull your plug when waiting for space

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <1394511196.4896.29.camel@marge.simpson.net>
Date:	Tue, 11 Mar 2014 05:13:16 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	tglx@...utronix.de
Subject: Re: [PATCH RT] fs: jbd2: pull your plug when waiting for space

On Mon, 2014-03-10 at 13:47 -0400, Theodore Ts'o wrote: 
> On Fri, Feb 21, 2014 at 02:54:12PM +0100, Mike Galbraith wrote:
> > 
> > ext3: dbench1 queues a buffer, blocks on journal mutex, it's plug is not
> > pulled.  dbench2 mutex owner is waiting for kjournald, who is waiting for
> > the buffer queued by dbench1.  Game over.
> 
> Where is in ext3/4 are we calling some function which could end up
> blocking on kjournald while we have the I/O queue plugged?  That
> sounds suspicious and potentially wrong.

I don't have the crash dumps and analysis handy, this was quite some
time ago.  Problem is that..

static inline void sched_submit_work(struct task_struct *tsk)
{
        if (!tsk->state || tsk_is_pi_blocked(tsk))
                return;
        /*
         * If we are going to sleep and we have plugged IO queued,
         * make sure to submit it to avoid deadlocks.
         */
        if (blk_needs_flush_plug(tsk))
                blk_schedule_flush_plug(tsk);
}

..tsk_is_pi_blocked(tsk) leaves us with IO queued, dependency on which
can (_did_ for ext[34] and xfs that I recall) end up with our waker
waiting on our IO.  There were other deadlock scenarios, not only the
one in the quoted text.

-Mike

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/