linux-kernel - Re: 2.6.18 ext3 panic.

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Date:	Thu, 12 Oct 2006 08:20:59 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Jan Kara <jack@...e.cz>
CC:	Eric Sandeen <esandeen@...hat.com>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Dave Jones <davej@...hat.com>, Andrew Morton <akpm@...l.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.18 ext3 panic.

Jan Kara wrote:

>> Talking with Stephen, it seemed like the page lock should synchronize these 
>> threads, but I've found that we can get to journal_dirty_data acting on the 
>> buffer heads w/o having the page locked...
>   Yes, PageLock should protect us. Where can we call
> journal_dirty_data() without PageLock? I see the following callers:
>   ext3_ordered_commit_write - should have PageLock
>   ext3_ordered_writepage - has PageLock
>   ext3_block_truncate_page - has PageLock
> 
>   And that are all callers from ext3. Am I missing something?
> 
> 								Honza

I put an assert about the page being locked in journal_dirty_data, and hit it 
right away.  I'll look a bit more but I think this is how I got there:


ext3_ordered_writepage <-- assert PageLocked
	...
	block_write_full_page
		__block_write_full_page
			unlock_page()
	...
	walk_page_buffers
		journal_dirty_data_fn
			ext3_journal_dirty_data
				journal_dirty_data <-- find page unlocked

there's a comment in ext3_ordered_writepage:

         /*
          * The page can become unlocked at any point now, and
          * truncate can then come in and change things.  So we
          * can't touch *page from now on.  But *page_bufs is
          * safe due to elevated refcount.
          */

-Eric
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