On Fri, 2018-01-12 at 10:06 -0500, Mike Snitzer wrote:
> I'm submitting this v5 with more feeling now ;)
Hello Mike,
Have these patches been tested with lockdep enabled? The following appeared in
the kernel log when after I started testing Jens' for-next tree of this morning:
======================================================
WARNING: possible circular locking dependency detected
4.15.0-rc7-dbg+ #1 Not tainted
------------------------------------------------------
02-mq/1211 is trying to acquire lock:
(&q->sysfs_lock){+.+.}, at: [<000000008b65bdad>] queue_attr_store+0x35/0x80
but task is already holding lock:
(kn->count#213){++++}, at: [<000000007a18ad18>] kernfs_fop_write+0xe5/0x190
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (kn->count#213){++++}:
kernfs_remove+0x1a/0x30
kobject_del.part.3+0xe/0x40
blk_unregister_queue+0xa7/0xe0
del_gendisk+0x12f/0x260
sd_remove+0x58/0xc0 [sd_mod]
device_release_driver_internal+0x15a/0x220
bus_remove_device+0xf4/0x170
device_del+0x12f/0x330
__scsi_remove_device+0xef/0x120 [scsi_mod]
scsi_forget_host+0x1b/0x60 [scsi_mod]
scsi_remove_host+0x6f/0x110 [scsi_mod]
0xffffffffc09ed6e4
process_one_work+0x21c/0x6d0
worker_thread+0x35/0x380
kthread+0x117/0x130
ret_from_fork+0x24/0x30
-> #0 (&q->sysfs_lock){+.+.}:
__mutex_lock+0x6c/0x9e0
queue_attr_store+0x35/0x80
kernfs_fop_write+0x109/0x190
__vfs_write+0x1e/0x130
vfs_write+0xb9/0x1b0
SyS_write+0x40/0xa0
entry_SYSCALL_64_fastpath+0x23/0x9a
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(kn->count#213);
lock(&q->sysfs_lock);
lock(kn->count#213);
lock(&q->sysfs_lock);
*** DEADLOCK ***
3 locks held by 02-mq/1211:
#0: (sb_writers#6){.+.+}, at: [<00000000afdb61d3>] vfs_write+0x17f/0x1b0
#1: (&of->mutex){+.+.}, at: [<00000000b291cabb>] kernfs_fop_write+0xdd/0x190
#2: (kn->count#213){++++}, at: [<000000007a18ad18>] kernfs_fop_write+0xe5/0x190
stack backtrace:
CPU: 2 PID: 1211 Comm: 02-mq Not tainted 4.15.0-rc7-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
Call Trace:
dump_stack+0x85/0xbf
print_circular_bug.isra.35+0x1d7/0x1e4
__lock_acquire+0x12af/0x1370
? lock_acquire+0xa8/0x230
lock_acquire+0xa8/0x230
? queue_attr_store+0x35/0x80
? queue_attr_store+0x35/0x80
__mutex_lock+0x6c/0x9e0
? queue_attr_store+0x35/0x80
? kernfs_fop_write+0xdd/0x190
? __mutex_lock+0x6c/0x9e0
? __mutex_lock+0x3d0/0x9e0
? lock_acquire+0xa8/0x230
? __lock_is_held+0x55/0x90
? queue_attr_store+0x35/0x80
queue_attr_store+0x35/0x80
kernfs_fop_write+0x109/0x190
__vfs_write+0x1e/0x130
? rcu_read_lock_sched_held+0x66/0x70
? rcu_sync_lockdep_assert+0x23/0x50
? __sb_start_write+0x152/0x1f0
? __sb_start_write+0x168/0x1f0
vfs_write+0xb9/0x1b0
SyS_write+0x40/0xa0
entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x7fab8be8d054
RSP: 002b:00007ffd39f0def8 EFLAGS: 00000246
Thanks,
Bart.
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