Re: [PATCH] nvme-multipath: fix lockdep warning on shutdown

[Hannes Reinecke <hare@suse.de>]

On 1/24/25 08:14, hare@kernel.org wrote:
> From: Hannes Reinecke <hare@kernel.org>
> 
> During shutdown of multipath devices lockdep complained about a
> potential circular locking:
> 
> WARNING: possible circular locking dependency detected
> (udev-worker)/2792 is trying to acquire lock:
> ffff8881012a4348 ((wq_completion)kblockd){+.+.}-{0:0}, at: touch_wq_lockdep_map+0
> x26/0x90
> 
> but task is already holding lock:
> ffff88811e4b7cc8 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_release+0x61/0x1a0
> which lock already depends on the new lock.
> 
> the existing dependency chain (in reverse order) is:
> -> #2 (&disk->open_mutex){+.+.}-{4:4}:
>          __mutex_lock+0xa5/0xe00
>         nvme_partition_scan_work+0x31/0x60
>          process_scheduled_works+0x37c/0x6f0
> -> #1 ((work_completion)(&head->partition_scan_work)){+.+.}-{0:0}:
>          process_scheduled_works+0x348/0x6f0
>          worker_thread+0x127/0x2a0
> -> #0 ((wq_completion)kblockd){+.+.}-{0:0}:
>          __lock_acquire+0x11f9/0x1790
>          lock_acquire+0x245/0x2d0
>          touch_wq_lockdep_map+0x3b/0x90
>          __flush_work+0x240/0x4b0
>          nvme_mpath_remove_disk+0x2b/0x50
>          nvme_free_ns_head+0x19/0x90
> 
> So the problem is that nvme_mpath_remove_disk() is called with the
> disk->open_mutex held, hence calling flush_work on partition_scan_work
> (which also will try to lock disk->open_mutex) will deadlock.
> Fix this by checking for NVME_NSHEAD_DISK_LIVE before trying to lock
> disk->open_mutex.
> 
> Fixes: 1f021341eef4 ("nvme-multipath: defer partition scanning")
> 
> Signed-off-by: Hannes Reinecke <hare@kernel.org>
> ---
>   block/blk-ioprio.c                |  6 ++++-
>   drivers/nvme/host/multipath.c     |  2 ++
>   drivers/nvme/target/core.c        | 42 +++++++++++++++----------------
>   drivers/nvme/target/io-cmd-bdev.c |  9 +++++++
>   4 files changed, 37 insertions(+), 22 deletions(-)
> 
Nice analysis, but wrong patch.

Please ignore.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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