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

From: Rong Chen
Date: Mon Aug 10 2020 - 01:22:31 EST



On 8/8/20 10:35 PM, Mike Snitzer wrote:
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?
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
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