On Sat, Oct 19, 2024 at 04:46:13PM -0600, Jens Axboe wrote:
> On 10/17/24 7:35 PM, Ming Lei wrote:
> > Recently we got several deadlock report[1][2][3] caused by blk_mq_freeze_queue
> > and blk_enter_queue().
> >
> > Turns out the two are just like one rwsem, so model them as rwsem for
> > supporting lockdep:
> >
> > 1) model blk_mq_freeze_queue() as down_write_trylock()
> > - it is exclusive lock, so dependency with blk_enter_queue() is covered
> > - it is trylock because blk_mq_freeze_queue() are allowed to run concurrently
> >
> > 2) model blk_enter_queue() as down_read()
> > - it is shared lock, so concurrent blk_enter_queue() are allowed
> > - it is read lock, so dependency with blk_mq_freeze_queue() is modeled
> > - blk_queue_exit() is often called from other contexts(such as irq), and
> > it can't be annotated as rwsem_release(), so simply do it in
> > blk_enter_queue(), this way still covered cases as many as possible
> >
> > NVMe is the only subsystem which may call blk_mq_freeze_queue() and
> > blk_mq_unfreeze_queue() from different context, so it is the only
> > exception for the modeling. Add one tagset flag to exclude it from
> > the lockdep support.
> >
> > With lockdep support, such kind of reports may be reported asap and
> > needn't wait until the real deadlock is triggered.
>
> I think this is a great idea. We've had way too many issues in this
> area, getting lockdep to grok it (and report issues) is the ideal way to
> avoid that, and even find issues we haven't come across yet.
So far, one main false positive is that the modeling becomes not
correct when calling blk_queue_start_drain() with setting disk state as
GD_DEAD or queue as QUEUE_FLAG_DYING, since __bio_queue_enter() or
blk_queue_enter() can return immediately in this situation.
[ 281.645392] ======================================================
[ 281.647189] WARNING: possible circular locking dependency detected
[ 281.648770] 6.11.0_nbd+ #405 Not tainted
[ 281.649171] ------------------------------------------------------
[ 281.649668] nvme/10551 is trying to acquire lock:
[ 281.650100] ffff938a5717e3e0 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: __flush_work+0x1d6/0x4d0
[ 281.650771]
but task is already holding lock:
[ 281.651442] ffff938a12206c48 (q->q_usage_counter){++++}-{0:0}, at: blk_queue_start_drain+0x12/0x40
[ 281.652085]
which lock already depends on the new lock.
[ 281.653061]
the existing dependency chain (in reverse order) is:
[ 281.653820]
-> #1 (q->q_usage_counter){++++}-{0:0}:
[ 281.654525] blk_try_enter_queue+0xc7/0x230
[ 281.654951] __submit_bio+0xa7/0x190
[ 281.655339] submit_bio_noacct_nocheck+0x1b2/0x400
[ 281.655779] __block_write_full_folio+0x1e7/0x400
[ 281.656212] write_cache_pages+0x62/0xb0
[ 281.656608] blkdev_writepages+0x56/0x90
[ 281.657007] do_writepages+0x76/0x270
[ 281.657389] __writeback_single_inode+0x5b/0x4c0
[ 281.657813] writeback_sb_inodes+0x22e/0x550
[ 281.658220] __writeback_inodes_wb+0x4c/0xf0
[ 281.658617] wb_writeback+0x193/0x3f0
[ 281.658995] wb_workfn+0x343/0x530
[ 281.659353] process_one_work+0x212/0x700
[ 281.659739] worker_thread+0x1ce/0x380
[ 281.660118] kthread+0xd2/0x110
[ 281.660460] ret_from_fork+0x31/0x50
[ 281.660818] ret_from_fork_asm+0x1a/0x30
[ 281.661192]
-> #0 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}:
[ 281.661876] __lock_acquire+0x15c0/0x23e0
[ 281.662254] lock_acquire+0xd8/0x300
[ 281.662603] __flush_work+0x1f2/0x4d0
[ 281.662954] wb_shutdown+0xa1/0xd0
[ 281.663285] bdi_unregister+0x92/0x250
[ 281.663632] del_gendisk+0x37b/0x3a0
[ 281.664017] nvme_mpath_shutdown_disk+0x58/0x60 [nvme_core]
[ 281.664453] nvme_ns_remove+0x17f/0x210 [nvme_core]
[ 281.664854] nvme_remove_namespaces+0xf7/0x150 [nvme_core]
[ 281.665304] nvme_do_delete_ctrl+0x71/0x90 [nvme_core]
[ 281.665728] nvme_delete_ctrl_sync+0x3f/0x50 [nvme_core]
[ 281.666159] nvme_sysfs_delete+0x38/0x50 [nvme_core]
[ 281.666569] kernfs_fop_write_iter+0x15c/0x210
[ 281.666953] vfs_write+0x2a7/0x540
[ 281.667281] ksys_write+0x75/0x100
[ 281.667607] do_syscall_64+0x95/0x180
[ 281.667948] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 281.668352]
other info that might help us debug this:
[ 281.669122] Possible unsafe locking scenario:
[ 281.669671] CPU0 CPU1
[ 281.670019] ---- ----
[ 281.670358] lock(q->q_usage_counter);
[ 281.670676] lock((work_completion)(&(&wb->dwork)->work));
[ 281.671186] lock(q->q_usage_counter);
[ 281.671628] lock((work_completion)(&(&wb->dwork)->work));
[ 281.672056]
*** DEADLOCK ***
thanks,
Ming
