Re: [PATCH 5.4, 5.8] dm: fix bio splitting and its bio completion order for regular IO

[Mike Snitzer <snitzer@redhat.com>]

On Mon, Sep 28 2020 at  1:52pm -0400,
Greg KH <gregkh@linuxfoundation.org> wrote:

> On Mon, Sep 28, 2020 at 07:31:44PM +0200, Greg KH wrote:
> > On Mon, Sep 28, 2020 at 11:29:41AM -0400, Mike Snitzer wrote:
> > > This backport applies (with mild offset) to both v5.4.67 and v5.8.11:
> > > 
> > > >From ee1dfad5325ff1cfb2239e564cd411b3bfe8667a Mon Sep 17 00:00:00 2001
> > > From: Mike Snitzer <snitzer@redhat.com>
> > > Date: Mon, 14 Sep 2020 13:04:19 -0400
> > > Subject: [PATCH] dm: fix bio splitting and its bio completion order for regular IO
> > > 
> > > dm_queue_split() is removed because __split_and_process_bio() _must_
> > > handle splitting bios to ensure proper bio submission and completion
> > > ordering as a bio is split.
> > > 
> > > Otherwise, multiple recursive calls to ->submit_bio will cause multiple
> > > split bios to be allocated from the same ->bio_split mempool at the same
> > > time. This would result in deadlock in low memory conditions because no
> > > progress could be made (only one bio is available in ->bio_split
> > > mempool).
> > > 
> > > This fix has been verified to still fix the loss of performance, due
> > > to excess splitting, that commit 120c9257f5f1 provided.
> > > 
> > > Fixes: 120c9257f5f1 ("Revert "dm: always call blk_queue_split() in dm_process_bio()"")
> > > Cc: stable@vger.kernel.org # 5.0+, requires custom backport due to 5.9 changes
> > > Reported-by: Ming Lei <ming.lei@redhat.com>
> > > Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> > 
> > What is the git id of this patch in Linus's tree?
> 
> I dug it up:
> 	ee1dfad5325f ("dm: fix bio splitting and its bio completion order for regular IO")

I thought this line was adequate in my original email:
"From ee1dfad5325ff1cfb2239e564cd411b3bfe8667a Mon Sep 17 00:00:00 2001"

Maybe it was too subtle?  For future knowledge, how would you like to
see the git id of Linus's tree referenced?

Thanks,
Mike