linux-ext4 - Re: [BUG] aborted ext4 leads to inifinity loop in balance_dirty

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Message-ID: <20111109111524.GA1025@quack.suse.cz>
Date:	Wed, 9 Nov 2011 12:15:24 +0100
From:	Jan Kara <jack@...e.cz>
To:	Kazuya Mio <k-mio@...jp.nec.com>
Cc:	Jan Kara <jack@...e.cz>, ext4 <linux-ext4@...r.kernel.org>,
	Theodore Tso <tytso@....edu>,
	Andreas Dilger <adilger@...ger.ca>
Subject: Re: [BUG] aborted ext4 leads to inifinity loop in
 balance_dirty_pages

On Wed 09-11-11 17:28:20, Kazuya Mio wrote:
> 2011/11/08 9:03, Jan Kara wrote:
> > On Fri 28-10-11 14:34:31, Kazuya Mio wrote:
> >> 2011/10/25 22:40, Jan Kara wrote:
> >>>   Please no. Generally this boils down to what do we do with dirty data
> >>> when there's error in writing them out. Currently we just throw them away
> >>> (e.g. in media error case) but I don't think that's a generally good thing
> >>> because e.g. admin may want to copy the data to other working storage or
> >>> so. So I think we should rather keep the data and provide a mechanism for
> >>> userspace to ask kernel to get rid of the data (so that we don't eventually
> >>> run OOM).
> >>
> >> I see. I agree with you.
> >>
> >>>> Do you have any ideas?
> >>>   So the question is what would you like to achieve. If you just want to
> >>> unblock a thread then a solution would be to make a thread at
> >>> balance_dirty_pages() killable. If generally you want to get rid of dirty
> >>> memory, then I don't have a really good answer but throwing dirty data away
> >>> seems like a bad answer to me.
> >>
> >> The problem is that we cannot unmount the corrupted filesystem due to
> >> un-killable dd process. We must bring down the system to resume the service
> >> with no dirty pages. I think it is important for the service continuity
> >> to be able to kill the thread handling in balance_dirty_pages().
> >    OK, attached are two patches based on latest Linus's tree that should
> > make your task killable. Can you test them?
> 
> I'm trying to reproduce now, but it's hard. Could you wait a few days?
  Sure, take as much time as you need.

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