Re: drivers/md/dm-mpath.c:524 multipath_clone_and_map() error: double unlocked 'm->lock' (orig line 516)

[Mike Snitzer]

On Sat, Aug 08 2020 at  8:10am -0400,
kernel test robot <lkp@xxxxxxxxx> wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   449dc8c97089a6e09fb2dac4d92b1b7ac0eb7c1e
> commit: 374117ad4736c5a4f8012cfe59fc07d9d58191d5 dm mpath: use double checked locking in fast path
> date:   4 weeks ago
> config: arm-randconfig-m031-20200808 (attached as .config)
> compiler: arm-linux-gnueabi-gcc (GCC) 9.3.0
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@xxxxxxxxx>

All 3 recent reports about smatch showing "double unlocked 'm->lock'"
appear to be bogus.  Think smatch is generating false positives (and
given "Old smatch warnings" it seems it has been doing so for some
time).

In addition, does lkp@xxxxxxxxx no longer test linux-next?  The dm-mpath
locking changes that were just merged into mainline have been in
linux-next since July 13.  Why were these tests only done against
mainline?

Mike



> New smatch warnings:
> drivers/md/dm-mpath.c:524 multipath_clone_and_map() error: double unlocked 'm->lock' (orig line 516)
> 
> Old smatch warnings:
> drivers/md/dm-mpath.c:446 choose_pgpath() error: double unlocked 'm->lock' (orig line 416)
> drivers/md/dm-mpath.c:457 choose_pgpath() error: double unlocked 'm->lock' (orig line 403)
> drivers/md/dm-mpath.c:525 multipath_clone_and_map() error: double unlocked 'm->lock' (orig line 516)
> drivers/md/dm-mpath.c:526 multipath_clone_and_map() error: double unlocked 'm->lock' (orig line 524)
> drivers/md/dm-mpath.c:626 __map_bio() error: double unlocked 'm->lock' (orig line 615)
> drivers/md/dm-mpath.c:627 __map_bio() error: double unlocked 'm->lock' (orig line 615)
> drivers/md/dm-mpath.c:628 __map_bio() error: double unlocked 'm->lock' (orig line 626)
> drivers/md/dm-mpath.c:629 __map_bio() error: double unlocked 'm->lock' (orig line 628)
> drivers/md/dm-mpath.c:1607 pg_init_done() error: double unlocked 'm->lock' (orig line 1560)
> drivers/md/dm-mpath.c:1707 multipath_end_io_bio() error: double unlocked 'm->lock' (orig line 1704)
> drivers/md/dm-mpath.c:1988 multipath_prepare_ioctl() error: double unlocked 'm->lock' (orig line 1984)
> drivers/md/dm-mpath.c:2012 multipath_prepare_ioctl() error: double unlocked 'm->lock' (orig line 2001)
> 
> vim +524 drivers/md/dm-mpath.c
> 
>    498	
>    499	/*
>    500	 * Map cloned requests (request-based multipath)
>    501	 */
>    502	static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
>    503					   union map_info *map_context,
>    504					   struct request **__clone)
>    505	{
>    506		struct multipath *m = ti->private;
>    507		size_t nr_bytes = blk_rq_bytes(rq);
>    508		struct pgpath *pgpath;
>    509		struct block_device *bdev;
>    510		struct dm_mpath_io *mpio = get_mpio(map_context);
>    511		struct request_queue *q;
>    512		struct request *clone;
>    513	
>    514		/* Do we need to select a new pgpath? */
>    515		pgpath = READ_ONCE(m->current_pgpath);
>  > 516		if (!pgpath || !mpath_double_check_test_bit(MPATHF_QUEUE_IO, m))
>    517			pgpath = choose_pgpath(m, nr_bytes);
>    518	
>    519		if (!pgpath) {
>    520			if (must_push_back_rq(m))
>    521				return DM_MAPIO_DELAY_REQUEUE;
>    522			dm_report_EIO(m);	/* Failed */
>    523			return DM_MAPIO_KILL;
>  > 524		} else if (mpath_double_check_test_bit(MPATHF_QUEUE_IO, m) ||
>    525			   mpath_double_check_test_bit(MPATHF_PG_INIT_REQUIRED, m)) {
>    526			pg_init_all_paths(m);
>    527			return DM_MAPIO_DELAY_REQUEUE;
>    528		}
>    529	
>    530		mpio->pgpath = pgpath;
>    531		mpio->nr_bytes = nr_bytes;
>    532	
>    533		bdev = pgpath->path.dev->bdev;
>    534		q = bdev_get_queue(bdev);
>    535		clone = blk_get_request(q, rq->cmd_flags | REQ_NOMERGE,
>    536				BLK_MQ_REQ_NOWAIT);
>    537		if (IS_ERR(clone)) {
>    538			/* EBUSY, ENODEV or EWOULDBLOCK: requeue */
>    539			if (blk_queue_dying(q)) {
>    540				atomic_inc(&m->pg_init_in_progress);
>    541				activate_or_offline_path(pgpath);
>    542				return DM_MAPIO_DELAY_REQUEUE;
>    543			}
>    544	
>    545			/*
>    546			 * blk-mq's SCHED_RESTART can cover this requeue, so we
>    547			 * needn't deal with it by DELAY_REQUEUE. More importantly,
>    548			 * we have to return DM_MAPIO_REQUEUE so that blk-mq can
>    549			 * get the queue busy feedback (via BLK_STS_RESOURCE),
>    550			 * otherwise I/O merging can suffer.
>    551			 */
>    552			return DM_MAPIO_REQUEUE;
>    553		}
>    554		clone->bio = clone->biotail = NULL;
>    555		clone->rq_disk = bdev->bd_disk;
>    556		clone->cmd_flags |= REQ_FAILFAST_TRANSPORT;
>    557		*__clone = clone;
>    558	
>    559		if (pgpath->pg->ps.type->start_io)
>    560			pgpath->pg->ps.type->start_io(&pgpath->pg->ps,
>    561						      &pgpath->path,
>    562						      nr_bytes);
>    563		return DM_MAPIO_REMAPPED;
>    564	}
>    565	
> 
> ---
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