On Mon, 2017-10-09 at 19:17 +0100, Lorenzo Pieralisi wrote:
> Hi,
>
> I have run into the lockdep warning below while running v4.14-rc3/rc4
> on an ARM64 defconfig Juno dev board - reporting it to check whether
> it is a known/genuine issue.
>
> Please let me know if you need further debug data or need some
> specific tests.
>
> Thanks,
> Lorenzo
>
> [ 6.209384] ======================================================
> [ 6.215569] WARNING: possible circular locking dependency detected
> [ 6.221755] 4.14.0-rc4 #54 Not tainted
> [ 6.225503] ------------------------------------------------------
> [ 6.231689] kworker/4:0H/32 is trying to acquire lock:
> [ 6.236830] ((&task->u.tk_work)){+.+.}, at: [<ffff0000080e64cc>]
> process_one_work+0x1cc/0x3f0
> [ 6.245472]
> but task is already holding lock:
> [ 6.251309] ("xprtiod"){+.+.}, at: [<ffff0000080e64cc>]
> process_one_work+0x1cc/0x3f0
> [ 6.259158]
> which lock already depends on the new lock.
>
> [ 6.267345]
> the existing dependency chain (in reverse order) is:
> [ 6.274836]
> -> #1 ("xprtiod"){+.+.}:
> [ 6.279903] lock_acquire+0x6c/0xb8
> [ 6.283914] flush_work+0x188/0x270
> [ 6.287926] __cancel_work_timer+0x120/0x198
> [ 6.292720] cancel_work_sync+0x10/0x18
> [ 6.297081] xs_destroy+0x34/0x58
> [ 6.300917] xprt_destroy+0x84/0x90
> [ 6.304927] xprt_put+0x34/0x40
> [ 6.308589] rpc_task_release_client+0x6c/0x80
> [ 6.313557] rpc_release_resources_task+0x2c/0x38
> [ 6.318786] __rpc_execute+0x9c/0x210
> [ 6.322971] rpc_async_schedule+0x10/0x18
> [ 6.327504] process_one_work+0x240/0x3f0
> [ 6.332036] worker_thread+0x48/0x420
> [ 6.336222] kthread+0x12c/0x158
> [ 6.339972] ret_from_fork+0x10/0x18
> [ 6.344068]
> -> #0 ((&task->u.tk_work)){+.+.}:
> [ 6.349920] __lock_acquire+0x12ec/0x14a8
> [ 6.354451] lock_acquire+0x6c/0xb8
> [ 6.358462] process_one_work+0x22c/0x3f0
> [ 6.362994] worker_thread+0x48/0x420
> [ 6.367180] kthread+0x12c/0x158
> [ 6.370929] ret_from_fork+0x10/0x18
> [ 6.375025]
> other info that might help us debug this:
>
> [ 6.383038] Possible unsafe locking scenario:
>
> [ 6.388962] CPU0 CPU1
> [ 6.393493] ---- ----
> [ 6.398023] lock("xprtiod");
> [ 6.401080] lock((&task-
> >u.tk_work));
> [ 6.407444] lock("xprtiod");
> [ 6.413024] lock((&task->u.tk_work));
> [ 6.416863]
> *** DEADLOCK ***
>
> [ 6.422789] 1 lock held by kworker/4:0H/32:
> [ 6.426972] #0: ("xprtiod"){+.+.}, at: [<ffff0000080e64cc>]
> process_one_work+0x1cc/0x3f0
> [ 6.435258]
> stack backtrace:
> [ 6.439618] CPU: 4 PID: 32 Comm: kworker/4:0H Not tainted 4.14.0-
> rc4 #54
> [ 6.446325] Hardware name: ARM Juno development board (r2) (DT)
> [ 6.452252] Workqueue: xprtiod rpc_async_schedule
> [ 6.456959] Call trace:
> [ 6.459406] [<ffff000008089430>] dump_backtrace+0x0/0x3c8
> [ 6.464810] [<ffff00000808980c>] show_stack+0x14/0x20
> [ 6.469866] [<ffff000008a01a30>] dump_stack+0xb8/0xf0
> [ 6.474922] [<ffff0000081194ac>] print_circular_bug+0x224/0x3a0
> [ 6.480849] [<ffff00000811a304>] check_prev_add+0x304/0x860
> [ 6.486426] [<ffff00000811c8c4>] __lock_acquire+0x12ec/0x14a8
> [ 6.492177] [<ffff00000811d144>] lock_acquire+0x6c/0xb8
> [ 6.497406] [<ffff0000080e652c>] process_one_work+0x22c/0x3f0
> [ 6.503156] [<ffff0000080e6738>] worker_thread+0x48/0x420
> [ 6.508560] [<ffff0000080ed5bc>] kthread+0x12c/0x158
> [ 6.513528] [<ffff000008084d48>] ret_from_fork+0x10/0x18
>
Adding Tejun and Lai, since this looks like a workqueue locking issue.
Cheers
Trond
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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