On Thu, Jun 14 2018 at 2:12P -0400,
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> On Thu, Jun 14 2018 at 4:19am -0400,
> Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> > Hi Neil,
> >
> > In commit 18a25da8 ("dm: ensure bio submission follows a depth-first
> > tree walk") you've added a call to bio_clone_bioset to
> > __split_and_process_bio. Unlike all other bio splitting code this
> > actually allocates a new bio_vec array instead of just splitting the bio
> > and the iterator. I can't actually find a good reason for that either
> > in a cursory review of the code, the commit or the comments.
> >
> > Do you remember why this can't just use bio_clone_fast?
>
> Your question caused me to revisit this code and it is suspect for a
> couple reasons:
>
> 1) I'm also not seeing why we need bio_clone_bioset()
The patch below seems to work fine (given quick testing).. It also has a
side-effect of not breaking integrity support (which commit 18a25da8
appears to do because it isn't accounting for any of the integrity stuff
bio_split, or dm.c:clone_bio, does).
FYI, my other concerns in my my previous reply were unfounded and due to
misreading the existing code.
Neil, please still feel free to have a look at this to see if you can
recall why you used bio_clone_bioset().
If in the end you agree that the following patch is fine please let me
know and I'll get a proper fix staged.
Thanks,
Mike
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 20a8d63..dfb4783 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1582,10 +1582,9 @@ static blk_qc_t __split_and_process_bio(struct mapped_device *md,
* the usage of io->orig_bio in dm_remap_zone_report()
* won't be affected by this reassignment.
*/
- struct bio *b = bio_clone_bioset(bio, GFP_NOIO,
- &md->queue->bio_split);
+ struct bio *b = bio_split(bio, bio_sectors(bio) - ci.sector_count,
+ GFP_NOIO, &md->queue->bio_split);
ci.io->orig_bio = b;
- bio_advance(bio, (bio_sectors(bio) - ci.sector_count) << 9);
bio_chain(b, bio);
ret = generic_make_request(bio);
break;
