Re: FAILED: patch "[PATCH] dm zoned: Fix target BIO completion handling" failed to apply to 4.19-stable tree

[Sasha Levin <sashal@kernel.org>]

On Tue, Dec 18, 2018 at 04:02:21PM +0100, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 4.19-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 d57f9da890696af1484f4a47f7f123560197865a Mon Sep 17 00:00:00 2001
>From: Damien Le Moal <damien.lemoal@wdc.com>
>Date: Fri, 30 Nov 2018 15:31:48 +0900
>Subject: [PATCH] dm zoned: Fix target BIO completion handling
>
>struct bioctx includes the ref refcount_t to track the number of I/O
>fragments used to process a target BIO as well as ensure that the zone
>of the BIO is kept in the active state throughout the lifetime of the
>BIO. However, since decrementing of this reference count is done in the
>target .end_io method, the function bio_endio() must be called multiple
>times for read and write target BIOs, which causes problems with the
>value of the __bi_remaining struct bio field for chained BIOs (e.g. the
>clone BIO passed by dm core is large and splits into fragments by the
>block layer), resulting in incorrect values and inconsistencies with the
>BIO_CHAIN flag setting. This is turn triggers the BUG_ON() call:
>
>BUG_ON(atomic_read(&bio->__bi_remaining) <= 0);
>
>in bio_remaining_done() called from bio_endio().
>
>Fix this ensuring that bio_endio() is called only once for any target
>BIO by always using internal clone BIOs for processing any read or
>write target BIO. This allows reference counting using the target BIO
>context counter to trigger the target BIO completion bio_endio() call
>once all data, metadata and other zone work triggered by the BIO
>complete.
>
>Overall, this simplifies the code too as the target .end_io becomes
>unnecessary and differences between read and write BIO issuing and
>completion processing disappear.
>
>Fixes: 3b1a94c88b79 ("dm zoned: drive-managed zoned block device target")
>Cc: stable@vger.kernel.org
>Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>Signed-off-by: Mike Snitzer <snitzer@redhat.com>

This patch depends on 092b5648760a ("dm zoned: target: use refcount_t
for dm zoned reference counters"), it might make sense to just take it
as is instead of backporting d57f9da89069.

--
Thanks,
Sasha