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@xxxxxxxxxx>
> > 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@xxxxxxxxxxxxxxx # 5.0+, requires custom backport due to 5.9 changes
> > Reported-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
>
> 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")
