linux-kernel - Re: an infinite loop in ext4 in 3.14

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Message-ID: <alpine.LRH.2.02.1404171833190.19030@file01.intranet.prod.int.rdu2.redhat.com>
Date:	Thu, 17 Apr 2014 18:36:38 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
cc:	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: an infinite loop in ext4 in 3.14



On Thu, 17 Apr 2014, Theodore Ts'o wrote:

> On Thu, Apr 17, 2014 at 03:23:13PM -0400, Mikulas Patocka wrote:
> > 
> > I hit a bug in ext4 - jbd2 was stuck in an infinite loop when remounting 
> > the root filesystem read-only during shutdown.
> 
> Is this at all repeatable?

No - it happened just once.

> I suspect what happened is that we're not
> checking the error return from jbd2_log_do_checkpoint(), and if it ran
> into an error doing the jbd2_log_do_checkpoint --- for example, if it

There were no I/O errors on the console when the lockup happened.

> wasn't able to write to the journal --- say, because __wait_cp_io()
> returned -EIO, we might be spinning in the while loop in jbd2_journal_flush:
> 
> > while (!err && journal->j_checkpoint_transactions != NULL) {
> 
> 
> (as you suspected).
> 
> I can add some error checking, but it would be interesting to know if
> you can easily reproduce the problem so we can confirm if that's what
> was really going on.

I can write a script that reboots the machine and run it overnight...

> Regards,
> 
> 						- Ted

Mikulas
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