The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 8dd601fa8317243be887458c49f6c29c2f3d719f Mon Sep 17 00:00:00 2001
From: NeilBrown neilb@suse.com Date: Thu, 15 Feb 2018 20:00:15 +1100 Subject: [PATCH] dm: correctly handle chained bios in dec_pending()
dec_pending() is given an error status (possibly 0) to be recorded against a bio. It can be called several times on the one 'struct dm_io', and it is careful to only assign a non-zero error to io->status. However when it then assigned io->status to bio->bi_status, it is not careful and could overwrite a genuine error status with 0.
This can happen when chained bios are in use. If a bio is chained beneath the bio that this dm_io is handling, the child bio might complete and set bio->bi_status before the dm_io completes.
This has been possible since chained bios were introduced in 3.14, and has become a lot easier to trigger with commit 18a25da84354 ("dm: ensure bio submission follows a depth-first tree walk") as that commit caused dm to start using chained bios itself.
A particular failure mode is that if a bio spans an 'error' target and a working target, the 'error' fragment will complete instantly and set the ->bi_status, and the other fragment will normally complete a little later, and will clear ->bi_status.
The fix is simply to only assign io_error to bio->bi_status when io_error is not zero.
Reported-and-tested-by: Milan Broz gmazyland@gmail.com Cc: stable@vger.kernel.org (v3.14+) Signed-off-by: NeilBrown neilb@suse.com Signed-off-by: Mike Snitzer snitzer@redhat.com
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index d6de00f367ef..68136806d365 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -903,7 +903,8 @@ static void dec_pending(struct dm_io *io, blk_status_t error) queue_io(md, bio); } else { /* done with normal IO or empty flush */ - bio->bi_status = io_error; + if (io_error) + bio->bi_status = io_error; bio_endio(bio); } }