linux-kernel - Re: Block layer projects that I haven't had time for

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Date:	Thu, 11 Dec 2014 02:14:34 -0800
From:	Kent Overstreet <kmo@...erainc.com>
To:	Dongsu Park <dongsu.park@...fitbricks.com>
Cc:	Ming Lin <mlin@...ggr.net>, linux-fsdevel@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: Block layer projects that I haven't had time for

On Thu, Dec 11, 2014 at 11:07:51AM +0100, Dongsu Park wrote:
> Hi Ming & Kent,
> 
> On 10.12.2014 23:11, Ming Lin wrote:
> > > On Wed, Dec 10, 2014 at 02:42:14PM -0800, Ming Lin wrote:
> > > Try this fix:
> > Yes, it fixed ext4 problem.
> 
> @kent: Thank you for the patch. Indeed it fixes the ext4 lockup I've seen.
> I've applied it to my tree, under the branch block-mpage-bvecs-for-next.
> See 0d2e05525a58 ("fs/ext4: fix a lockup when writing blocks into ext4
> rootfs") <https://github.com/dongsupark/linux/commit/0d2e05525a58>.
> 
> After that of course, more bugs start to appear, e.g. crash with virtio-blk,
> like we'd have opened a can of worms. ;-)

Yeah :) You'll need to audit every usage of bio_for_each_segment() to figure out
which ones need converting to bio_for_each_page(). I did some of this - but just
enough to get it working for me, and I haven't worked on that code since at
least 3.14 so really everything needs to be audited.

Hopefully in the future a lot of stuff could be converted to
bio_for_each_segment() and changed to use more efficient algorithms, but that
will be a lot more work. With bio_for_each_page() it shouldn't be too hard to
get it stable, though.
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