Re: 4.1-rc2 dm-multipath-mq kernel warning

[Mike Snitzer <snitzer@redhat.com>]

On Wed, May 27 2015 at 11:33am -0400,
Bart Van Assche <bart.vanassche@sandisk.com> wrote:

> On 05/27/15 17:29, Bart Van Assche wrote:
> >On 05/27/15 14:57, Mike Snitzer wrote:
> >>Looks like Junichi likely fixed this issue you reported, please try this
> >>patch: https://patchwork.kernel.org/patch/6487321/
> >
> >Hello Mike,
> >
> >On a setup on which an I/O verification test passes with
> >blk-mq/scsi-mq/dm-mq disabled, this is what fio reports after a few
> >minutes with scsi-mq and dm-mq enabled:
> >
> >test: Laying out IO file(s) (1 file(s) / 10MB)
> >fio: io_u error on file /mnt/test.0.0: Input/output error: write
> >offset=8327168, buflen=4096
> >fio: io_u error on file /mnt/test.0.0: Input/output error: write
> >offset=9007104, buflen=4096
> >fio: pid=4568, err=5/file:io_u.c:1564, func=io_u error,
> >error=Input/output error

I'll look closer at this.. so NULL pointer is fixed but this test hits
IO errors.

> (replying to my own e-mail)
> 
> BTW, on the same test setup kmemleak reports several memory leaks,
> e.g. this one:
> 
> unreferenced object 0xffff88009b14e2b0 (size 16):
>   comm "fio", pid 4274, jiffies 4294978034 (age 1253.210s)
>   hex dump (first 16 bytes):
>     40 12 f3 99 01 88 ff ff 00 10 00 00 00 00 00 00  @...............
>   backtrace:
>     [<ffffffff81600029>] kmemleak_alloc+0x49/0xb0
>     [<ffffffff811679a8>] kmem_cache_alloc+0xf8/0x160
>     [<ffffffff8111c950>] mempool_alloc_slab+0x10/0x20
>     [<ffffffff8111cb37>] mempool_alloc+0x57/0x150
>     [<ffffffffa04d2b61>] __multipath_map.isra.17+0xe1/0x220 [dm_multipath]
>     [<ffffffffa04d2cb5>] multipath_clone_and_map+0x15/0x20 [dm_multipath]
>     [<ffffffffa02889b5>] map_request.isra.39+0xd5/0x220 [dm_mod]
>     [<ffffffffa028b0e4>] dm_mq_queue_rq+0x134/0x240 [dm_mod]
>     [<ffffffff812cccb5>] __blk_mq_run_hw_queue+0x1d5/0x380
>     [<ffffffff812ccaa5>] blk_mq_run_hw_queue+0xc5/0x100
>     [<ffffffff812ce350>] blk_sq_make_request+0x240/0x300
>     [<ffffffff812c0f30>] generic_make_request+0xc0/0x110
>     [<ffffffff812c0ff2>] submit_bio+0x72/0x150
>     [<ffffffff811c07cb>] do_blockdev_direct_IO+0x1f3b/0x2da0
>     [<ffffffff811c166e>] __blockdev_direct_IO+0x3e/0x40
>     [<ffffffff8120aa1a>] ext4_direct_IO+0x1aa/0x390

Would appear there is potential for an early return from
dm-mpath.c:__multipath_map() to leak the dm_mpath_io.

Please add this patch:

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 6395347..eff7bdd 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -429,9 +429,11 @@ static int __multipath_map(struct dm_target *ti, struct request *clone,
 		/* blk-mq request-based interface */
 		*__clone = blk_get_request(bdev_get_queue(bdev),
 					   rq_data_dir(rq), GFP_ATOMIC);
-		if (IS_ERR(*__clone))
+		if (IS_ERR(*__clone)) {
 			/* ENOMEM, requeue */
+			clear_mapinfo(m, map_context);
 			return r;
+		}
 		(*__clone)->bio = (*__clone)->biotail = NULL;
 		(*__clone)->rq_disk = bdev->bd_disk;
 		(*__clone)->cmd_flags |= REQ_FAILFAST_TRANSPORT;