new patchset to eliminate DM's use of BIOSET_NEED_RESCUER [was: Re: [PATCH 00/13] block: assorted cleanup for bio splitting and cloning.]

[Mike Snitzer]

On Tue, Nov 21 2017 at  7:43am -0500,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
 
> Decided it a better use of my time to review and then hopefully use the
> block-core's bio splitting infrastructure in DM.  Been meaning to do
> that for quite a while anyway.  This mail from you just made it all the
> more clear that needs doing:
> https://www.redhat.com/archives/dm-devel/2017-September/msg00098.html
> 
> So I will start here on this patch you proposed:
> https://www.redhat.com/archives/dm-devel/2017-September/msg00091.html
> (of note, this patch slipped through the cracks because I was recovering
> from injury when it originally came through).
> 
> Once DM is using q->bio_split I'll come back to this patch (aka
> "[1]") as a starting point for the follow-on work to remove DM's use of
> BIOSET_NEED_RESCUER:
> https://www.redhat.com/archives/dm-devel/2017-August/msg00315.html

Hey Neil,

Good news!  All your code works ;)

(well after 1 fixup due to a cut-n-paste bug.. the code you added to
dm_wq_work() to process the md->rescued bio_list was operating on
the md->deferred bio_list due to cut-n-paste from code you copied from
just below it)

I split your code out some to make it more reviewable.  I also tweaked
headers accordingly.

Please see this branch (which _will_ get rebased between now and the
4.16 merge window):
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.16

I successfully tested these changes using Mikulas' test program that
reproduces the snapshot deadlock:
https://www.redhat.com/archives/dm-devel/2017-January/msg00064.html

I'll throw various other DM testsuites at it to verify they all look
good (e.g. thinp, cache, multipath).

I'm open to all suggestions about changes you'd like to see (either to
these patches or anything you'd like to layer ontop of them).

Thanks for all your work, much appreciated!
Mike