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Date:   Mon, 10 Aug 2020 13:13:52 +0800
From:   Rong Chen <rong.a.chen@...el.com>
To:     Mike Snitzer <snitzer@...hat.com>,
        kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [kbuild-all] Re: drivers/md/dm-mpath.c:524
 multipath_clone_and_map() error: double unlocked 'm->lock' (orig line 516)



On 8/8/20 10:35 PM, Mike Snitzer wrote:
> On Sat, Aug 08 2020 at  8:10am -0400,
> kernel test robot <lkp@...el.com> 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@...el.com>
> 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@...el.com 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?
Hi Mike,

kernel test robot still test linux-next, but the bisection worked on 
linus/master and didn't check the fix in linux-next,
we'll optimize the bisection to avoid reporting this kind of problem.

Best Regards,
Rong Chen

>
> 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	
>>
>> ---
>> 0-DAY CI Kernel Test Service, Intel Corporation
>> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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