linux-ext4 - Re: [PATCH 1/3] add releasepage hooks to block devices which can be used by file systems

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Date:	Mon, 5 Jan 2009 11:05:14 -0500
From:	Theodore Tso <tytso@....edu>
To:	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/3] add releasepage hooks to block devices which can
	be used by file systems

On Mon, Jan 05, 2009 at 05:16:08PM +0900, Toshiyuki Okajima wrote:
> 
> I was confirming whether the kernel to which your new patch is
> applied can run without trouble. But unfortunately, I got a hangup
> problem. Now I am investigating the root cause.  After I
> investigated it for a little time, I think calling log_wait_commit()
> from journal_try_to_free_buffers() can cause it.  

Sounds like a deadlock caused by the fact that we're no longer masking
__GFP_WAIT, probably on journal->j_wait_done_commit.  Presumably the
system came under pressure during a commit operation, which makes
sense, and so we ended up with a deadlock between kjournald and
kswapd.  The fix is pretty simple; we just need to mask out the
__GFP_WAIT in the filesystem-specific callback, since this is a
restriction imposed by the filesystem's use of the jbd/jbd2 layer.

	    	       	   		       - Ted
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