Re: net/sunrpc: v4.14-rc4 lockdep warning

[Trond Myklebust <trondmy@primarydata.com>]

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@primarydata.com