FAILED: patch "[PATCH] dm: fix NULL pointer when clone_and_map_rq returns" failed to apply to 4.0-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.0-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 3a1407559a593d4360af12dd2df5296bf8eb0d28 Mon Sep 17 00:00:00 2001
From: Junichi Nomura <j-nomura@ce.jp.nec.com>
Date: Wed, 27 May 2015 04:22:07 +0000
Subject: [PATCH] dm: fix NULL pointer when clone_and_map_rq returns
 !DM_MAPIO_REMAPPED

When stacking request-based DM on blk_mq device, request cloning and
remapping are done in a single call to target's clone_and_map_rq().
The clone is allocated and valid only if clone_and_map_rq() returns
DM_MAPIO_REMAPPED.

The "IS_ERR(clone)" check in map_request() does not cover all the
!DM_MAPIO_REMAPPED cases that are possible (E.g. if underlying devices
are not ready or unavailable, clone_and_map_rq() may return
DM_MAPIO_REQUEUE without ever having established an ERR_PTR).  Fix this
by explicitly checking for a return that is not DM_MAPIO_REMAPPED in
map_request().

Without this fix, DM core may call setup_clone() for a NULL clone
and oops like this:

   BUG: unable to handle kernel NULL pointer dereference at 0000000000000068
   IP: [<ffffffff81227525>] blk_rq_prep_clone+0x7d/0x137
   ...
   CPU: 2 PID: 5793 Comm: kdmwork-253:3 Not tainted 4.0.0-nm #1
   ...
   Call Trace:
    [<ffffffffa01d1c09>] map_tio_request+0xa9/0x258 [dm_mod]
    [<ffffffff81071de9>] kthread_worker_fn+0xfd/0x150
    [<ffffffff81071cec>] ? kthread_parkme+0x24/0x24
    [<ffffffff81071cec>] ? kthread_parkme+0x24/0x24
    [<ffffffff81071fdd>] kthread+0xe6/0xee
    [<ffffffff81093a59>] ? put_lock_stats+0xe/0x20
    [<ffffffff81071ef7>] ? __init_kthread_worker+0x5b/0x5b
    [<ffffffff814c2d98>] ret_from_fork+0x58/0x90
    [<ffffffff81071ef7>] ? __init_kthread_worker+0x5b/0x5b

Fixes: e5863d9ad ("dm: allocate requests in target when stacking on blk-mq devices")
Reported-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # 4.0+

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 0bf79a0bad37..1c62ed8d09f4 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1972,8 +1972,8 @@ static int map_request(struct dm_rq_target_io *tio, struct request *rq,
 			dm_kill_unmapped_request(rq, r);
 			return r;
 		}
-		if (IS_ERR(clone))
-			return DM_MAPIO_REQUEUE;
+		if (r != DM_MAPIO_REMAPPED)
+			return r;
 		if (setup_clone(clone, rq, tio, GFP_ATOMIC)) {
 			/* -ENOMEM */
 			ti->type->release_clone_rq(clone);