linux-ext4 - Re: Is warn_on() right reply for i/o error?

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Message-ID: <20140729120555.GB5944@quack.suse.cz>
Date:	Tue, 29 Jul 2014 14:05:55 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, jack@...e.cz
Subject: Re: Is warn_on() right reply for i/o error?

On Thu 24-07-14 15:29:38, Ted Tso wrote:
> On Thu, Jul 24, 2014 at 05:27:22PM +0200, Pavel Machek wrote:
> > Hi!
> > 
> > Just... I know, I should not be unscrewing hard drive cover while
> > operating.
> > 
> > But on the other hand... WARN_ON() does not sound like right reply for
> > a disk failure... right?
> 
> Actually, it can be worse than that.  If a hard drive disappears out
> from under you while writeback is happening, it's possible to get
> crashes in bdi_writeack_workfn() because you can have races between
> bdi_unregister() and bdi_writeback_workfn(), since the latter requeues
> itself and flush_delayed_work() can return while
> bdi_writeback_workfn() is still executing.
  This should be fixed by 5acda9d12dcf1ad0d9a5a2a7c646de3472fa7555 I wrote
in April. But there are certainly other races in that code...

> This looks like it's a related problem, where the block device gets
> unregistered (and this happens in the block device layer without it
> telling the file system that the disk drive is about to disappear out
> from under it), and occasionally, Bad Stuff Happens.  :-(
  Yeah.

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