linux-ext4 - Re: Help on Implementation of EXT3 type Ordered Mode in EXT4

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Date:	Mon, 29 Mar 2010 17:45:34 +0200
From:	Jan Kara <jack@...e.cz>
To:	Kailas Joshi <kailas.joshi@...il.com>
Cc:	tytso@....edu, linux-ext4@...r.kernel.org,
	Jiaying Zhang <jiayingz@...gle.com>
Subject: Re: Help on Implementation of EXT3 type Ordered Mode in EXT4

  Hi,

On Tue 23-03-10 16:11:45, Kailas Joshi wrote:
> I have Lock Debugging enables but that didn't give any warnings.
> However, when I did echo "w" >/proc/sysrq-trigger after system lockup,
> I got the stack trace for locked up process.
> 
> Following are the stack traces of the processes (I suspect) resulting
> in total system lockup -
  <snip>

  So kjournald is waiting on a page lock and everyone else waits for
kjournald to finish committing or for page lock as well. The strange thing
is that I don't see anybody who could hold the page lock everyone is
waiting on. So I think further debugging should go in this direction - find
out on which page do we wait and who is holding it's lock (you'd need to
add tracking of page lock owner but that shouldn't be too hard).

> I have few questions here.
> I guess process named jbd2/sdb1-8 is kjournald thread. But what is
  Yes.

> flush-8:16 process? Is it the kernel thread for periodically writing
> dirty pages to disk?
  Yes.

> Is it the case that these threads are running concurrently at certain
> time and are trying to get lock on same pages resulting into deadlock?
  It should not happen - they should always acquire page lock in
index-increasing order so that way deadlocks should be avoided...

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