linux-kernel - Re: next/mmotm: ext4 causes !rwsem_is

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Message-ID: <20120927212708.GA10044@thunk.org>
Date:	Thu, 27 Sep 2012 17:27:08 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: next/mmotm: ext4 causes !rwsem_is_locked warnings

On Thu, Sep 27, 2012 at 02:05:00PM -0700, Hugh Dickins wrote:
> Hi Ted,
> 
> mmotm (or next) now gives me lots of WARNING at fs/fs-writeback.c:1312 from
> writeback_inodes_sb_nr().  That's WARN_ON(!rwsem_is_locked(&sb->s_umount))
> (some useful safety from hch) in writeback_inodes_sb_nr().
> 
> Your commit 40e684e5c597a98996cf4616e31fb2581ec82060
> "ext4: fix potential deadlock in ext4_nonda_switch()" needs more change
> to fs/fs-writeback.c.  I guess I'm the only one using a nearly full ext4.
> 
> I am, of course, applying the patch at the bottom to my tree for now;
> but I think you'd do better not to eliminate that check.  Maybe add a
> special wb_reason for your case, and skip rwsem check in that case.

Yeah, we were just discussing this on another thread.  I didn't think
of the option of creating a new special wb_reason option, but that's a
much better option than the other ones I had been considering, so I
think I will give that a try.   Thanks for the suggestion!!

      	     	       	 	       - Ted
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