[4.2.y-ckt stable] Patch "dm: fix dm_rq_target_io leak on faults with .request_fn DM w/ blk-mq paths" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    dm: fix dm_rq_target_io leak on faults with .request_fn DM w/ blk-mq paths

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 234fc39c1e719f587fa6b6432cb592bec8937346 Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer at redhat.com>
Date: Sun, 21 Feb 2016 19:09:22 -0500
Subject: dm: fix dm_rq_target_io leak on faults with .request_fn DM w/ blk-mq
 paths

commit 4328daa2e79ed904a42ce00a9f38b9c36b44b21a upstream.

Using request-based DM mpath configured with the following stacking
(.request_fn DM mpath ontop of scsi-mq paths):

echo Y > /sys/module/scsi_mod/parameters/use_blk_mq
echo N > /sys/module/dm_mod/parameters/use_blk_mq

'struct dm_rq_target_io' would leak if a request is requeued before a
blk-mq clone is allocated (or fails to allocate).  free_rq_tio()
wasn't being called.

kmemleak reported:

unreferenced object 0xffff8800b90b98c0 (size 112):
  comm "kworker/7:1H", pid 5692, jiffies 4295056109 (age 78.589s)
  hex dump (first 32 bytes):
    00 d0 5c 2c 03 88 ff ff 40 00 bf 01 00 c9 ff ff  ..\,.... at .......
    e0 d9 b1 34 00 88 ff ff 00 00 00 00 00 00 00 00  ...4............
  backtrace:
    [<ffffffff81672b6e>] kmemleak_alloc+0x4e/0xb0
    [<ffffffff811dbb63>] kmem_cache_alloc+0xc3/0x1e0
    [<ffffffff8117eae5>] mempool_alloc_slab+0x15/0x20
    [<ffffffff8117ec1e>] mempool_alloc+0x6e/0x170
    [<ffffffffa00029ac>] dm_old_prep_fn+0x3c/0x180 [dm_mod]
    [<ffffffff812fbd78>] blk_peek_request+0x168/0x290
    [<ffffffffa0003e62>] dm_request_fn+0xb2/0x1b0 [dm_mod]
    [<ffffffff812f66e3>] __blk_run_queue+0x33/0x40
    [<ffffffff812f9585>] blk_delay_work+0x25/0x40
    [<ffffffff81096fff>] process_one_work+0x14f/0x3d0
    [<ffffffff81097715>] worker_thread+0x125/0x4b0
    [<ffffffff8109ce88>] kthread+0xd8/0xf0
    [<ffffffff8167cb8f>] ret_from_fork+0x3f/0x70
    [<ffffffffffffffff>] 0xffffffffffffffff

crash> struct -o dm_rq_target_io
struct dm_rq_target_io {
    ...
}
SIZE: 112

Fixes: e5863d9ad7 ("dm: allocate requests in target when stacking on blk-mq devices")
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/dm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index e0bf361..3f82998 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1161,6 +1161,8 @@ static void dm_unprep_request(struct request *rq)

 	if (clone)
 		free_rq_clone(clone);
+	else if (!tio->md->queue->mq_ops)
+		free_rq_tio(tio);
 }

 /*
--
2.7.0