linux-kernel - Re: fs: Inode cache scalability V3

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Message-ID: <20101013233647.GA18691@infradead.org>
Date:	Wed, 13 Oct 2010 19:36:48 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	axboe@...nel.dk
Subject: Re: fs: Inode cache scalability V3

On Wed, Oct 13, 2010 at 05:46:09PM -0400, Christoph Hellwig wrote:
> On Wed, Oct 13, 2010 at 11:58:45AM -0400, Christoph Hellwig wrote:
> > 
> > It's 100% reproducible on my kvm VM.  The bug is the assert_spin_locked
> > in redirty_tail.  I really can't find a way how we reach it without
> > d_lock so this really confuses me.
> 
> We are for some reason getting a block device inode that is on the
> dirty list of a bdi that it doesn't point to.  Still trying to figure
> out how exactly that happens.

It's because __blkdev_put reset the bdi on the mapping, and bdev inodes
are still special cased to not use s_bdi unlike everybody else.  So
we keep switch between different bdis that get locked.

I wonder what's a good workaround for that.  Just flushing out all
dirty state of a block device inode on last close would fix, but we'd
still have all the dragons hidden underneath until we finally sort
out the bdi reference mess.

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