FAILED: patch "[PATCH] dm: correctly handle chained bios in dec_pending()" failed to apply to 4.4-stable tree

FAILED: patch "[PATCH] dm: correctly handle chained bios in dec_pending()" failed to apply to 4.4-stable tree

[gregkh]

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);
 		}
 	}

[PATCH - 4.4-stable] dm: correctly handle chained bios in dec_pending()

[NeilBrown]

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Commit 8dd601fa8317243be887458c49f6c29c2f3d719f upstream.

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>
---
 drivers/md/dm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 9ec6948e3b8b..3d9a80759d95 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -974,7 +974,8 @@ static void dec_pending(struct dm_io *io, int error)
 		} else {
 			/* done with normal IO or empty flush */
 			trace_block_bio_complete(md->queue, bio, io_error);
-			bio->bi_error = io_error;
+			if (io_error)
+				bio->bi_error = io_error;
 			bio_endio(bio);
 		}
 	}
-- 
2.14.0.rc0.dirty


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Re: [PATCH - 4.4-stable] dm: correctly handle chained bios in dec_pending()

[Greg KH]

On Wed, Feb 21, 2018 at 07:06:39AM +1100, NeilBrown wrote:
> 
> Commit 8dd601fa8317243be887458c49f6c29c2f3d719f upstream.

Thanks for this, and the 4.9 backport, both now applied.

greg k-h