* Xen Linux deadlock
@ 2017-06-07 15:05 Andre Przywara
2017-06-07 15:51 ` Juergen Gross
0 siblings, 1 reply; 2+ messages in thread
From: Andre Przywara @ 2017-06-07 15:05 UTC (permalink / raw)
To: xen-devel
Cc: Juergen Gross, Julien Grall, Stefano Stabellini, Boris Ostrovsky
Hi,
when booting Linux 4.12-rc4 as Dom0 under a recent Xen HV I saw the
following lockdep splat after running xencommons start:
root@junor1:~# bash /etc/init.d/xencommons start
Setting domain 0 name, domid and JSON config...
[ 247.979498] ======================================================
[ 247.985688] WARNING: possible circular locking dependency detected
[ 247.991882] 4.12.0-rc4-00022-gc4b25c0 #575 Not tainted
[ 247.997040] ------------------------------------------------------
[ 248.003232] xenbus/91 is trying to acquire lock:
[ 248.007875] (&u->msgbuffer_mutex){+.+.+.}, at: [<ffff00000863e904>]
xenbus_dev_queue_reply+0x3c/0x230
[ 248.017163]
[ 248.017163] but task is already holding lock:
[ 248.023096] (xb_write_mutex){+.+...}, at: [<ffff00000863a940>]
xenbus_thread+0x5f0/0x798
[ 248.031267]
[ 248.031267] which lock already depends on the new lock.
[ 248.031267]
[ 248.039615]
[ 248.039615] the existing dependency chain (in reverse order) is:
[ 248.047176]
[ 248.047176] -> #1 (xb_write_mutex){+.+...}:
[ 248.052943] __lock_acquire+0x1728/0x1778
[ 248.057498] lock_acquire+0xc4/0x288
[ 248.061630] __mutex_lock+0x84/0x868
[ 248.065755] mutex_lock_nested+0x3c/0x50
[ 248.070227] xs_send+0x164/0x1f8
[ 248.074015] xenbus_dev_request_and_reply+0x6c/0x88
[ 248.079427] xenbus_file_write+0x260/0x420
[ 248.084073] __vfs_write+0x48/0x138
[ 248.088113] vfs_write+0xa8/0x1b8
[ 248.091983] SyS_write+0x54/0xb0
[ 248.095768] el0_svc_naked+0x24/0x28
[ 248.099897]
[ 248.099897] -> #0 (&u->msgbuffer_mutex){+.+.+.}:
[ 248.106088] print_circular_bug+0x80/0x2e0
[ 248.110730] __lock_acquire+0x1768/0x1778
[ 248.115288] lock_acquire+0xc4/0x288
[ 248.119417] __mutex_lock+0x84/0x868
[ 248.123545] mutex_lock_nested+0x3c/0x50
[ 248.128016] xenbus_dev_queue_reply+0x3c/0x230
[ 248.133005] xenbus_thread+0x788/0x798
[ 248.137306] kthread+0x110/0x140
[ 248.141087] ret_from_fork+0x10/0x40
[ 248.145214]
[ 248.145214] other info that might help us debug this:
[ 248.145214]
[ 248.153383] Possible unsafe locking scenario:
[ 248.153383]
[ 248.159403] CPU0 CPU1
[ 248.163960] ---- ----
[ 248.168518] lock(xb_write_mutex);
[ 248.172045] lock(&u->msgbuffer_mutex);
[ 248.178500] lock(xb_write_mutex);
[ 248.184514] lock(&u->msgbuffer_mutex);
[ 248.188470]
[ 248.188470] *** DEADLOCK ***
[ 248.188470]
[ 248.194578] 2 locks held by xenbus/91:
[ 248.198360] #0: (xs_response_mutex){+.+...}, at:
[<ffff00000863a7b0>] xenbus_thread+0x460/0x798
[ 248.207218] #1: (xb_write_mutex){+.+...}, at: [<ffff00000863a940>]
xenbus_thread+0x5f0/0x798
[ 248.215818]
[ 248.215818] stack backtrace:
[ 248.220293] CPU: 0 PID: 91 Comm: xenbus Not tainted
4.12.0-rc4-00022-gc4b25c0 #575
[ 248.227858] Hardware name: ARM Juno development board (r1) (DT)
[ 248.233792] Call trace:
[ 248.236289] [<ffff00000808a748>] dump_backtrace+0x0/0x270
[ 248.241707] [<ffff00000808aa94>] show_stack+0x24/0x30
[ 248.246782] [<ffff0000084caa98>] dump_stack+0xb8/0xf0
[ 248.251859] [<ffff000008139068>] print_circular_bug+0x1f8/0x2e0
[ 248.257787] [<ffff00000813c090>] __lock_acquire+0x1768/0x1778
[ 248.263548] [<ffff00000813c90c>] lock_acquire+0xc4/0x288
[ 248.268882] [<ffff000008bdb28c>] __mutex_lock+0x84/0x868
[ 248.274219] [<ffff000008bdbaac>] mutex_lock_nested+0x3c/0x50
[ 248.279889] [<ffff00000863e904>] xenbus_dev_queue_reply+0x3c/0x230
[ 248.286081] [<ffff00000863aad8>] xenbus_thread+0x788/0x798
[ 248.291585] [<ffff000008108070>] kthread+0x110/0x140
[ 248.296572] [<ffff000008083710>] ret_from_fork+0x10/0x40
Apparently it's not easily reproducible, but Julien confirmed that the
dead lock condition as reported above is indeed in the Linux code.
Does anyone has an idea of how to fix this?
Cheers,
Andre.
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Xen-devel@lists.xen.org
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^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Xen Linux deadlock
2017-06-07 15:05 Xen Linux deadlock Andre Przywara
@ 2017-06-07 15:51 ` Juergen Gross
0 siblings, 0 replies; 2+ messages in thread
From: Juergen Gross @ 2017-06-07 15:51 UTC (permalink / raw)
To: Andre Przywara, xen-devel
Cc: Julien Grall, Stefano Stabellini, Boris Ostrovsky
On 07/06/17 17:05, Andre Przywara wrote:
> Hi,
>
> when booting Linux 4.12-rc4 as Dom0 under a recent Xen HV I saw the
> following lockdep splat after running xencommons start:
>
> root@junor1:~# bash /etc/init.d/xencommons start
> Setting domain 0 name, domid and JSON config...
> [ 247.979498] ======================================================
> [ 247.985688] WARNING: possible circular locking dependency detected
> [ 247.991882] 4.12.0-rc4-00022-gc4b25c0 #575 Not tainted
> [ 247.997040] ------------------------------------------------------
> [ 248.003232] xenbus/91 is trying to acquire lock:
> [ 248.007875] (&u->msgbuffer_mutex){+.+.+.}, at: [<ffff00000863e904>]
> xenbus_dev_queue_reply+0x3c/0x230
> [ 248.017163]
> [ 248.017163] but task is already holding lock:
> [ 248.023096] (xb_write_mutex){+.+...}, at: [<ffff00000863a940>]
> xenbus_thread+0x5f0/0x798
> [ 248.031267]
> [ 248.031267] which lock already depends on the new lock.
> [ 248.031267]
> [ 248.039615]
> [ 248.039615] the existing dependency chain (in reverse order) is:
> [ 248.047176]
> [ 248.047176] -> #1 (xb_write_mutex){+.+...}:
> [ 248.052943] __lock_acquire+0x1728/0x1778
> [ 248.057498] lock_acquire+0xc4/0x288
> [ 248.061630] __mutex_lock+0x84/0x868
> [ 248.065755] mutex_lock_nested+0x3c/0x50
> [ 248.070227] xs_send+0x164/0x1f8
> [ 248.074015] xenbus_dev_request_and_reply+0x6c/0x88
> [ 248.079427] xenbus_file_write+0x260/0x420
> [ 248.084073] __vfs_write+0x48/0x138
> [ 248.088113] vfs_write+0xa8/0x1b8
> [ 248.091983] SyS_write+0x54/0xb0
> [ 248.095768] el0_svc_naked+0x24/0x28
> [ 248.099897]
> [ 248.099897] -> #0 (&u->msgbuffer_mutex){+.+.+.}:
> [ 248.106088] print_circular_bug+0x80/0x2e0
> [ 248.110730] __lock_acquire+0x1768/0x1778
> [ 248.115288] lock_acquire+0xc4/0x288
> [ 248.119417] __mutex_lock+0x84/0x868
> [ 248.123545] mutex_lock_nested+0x3c/0x50
> [ 248.128016] xenbus_dev_queue_reply+0x3c/0x230
> [ 248.133005] xenbus_thread+0x788/0x798
> [ 248.137306] kthread+0x110/0x140
> [ 248.141087] ret_from_fork+0x10/0x40
> [ 248.145214]
> [ 248.145214] other info that might help us debug this:
> [ 248.145214]
> [ 248.153383] Possible unsafe locking scenario:
> [ 248.153383]
> [ 248.159403] CPU0 CPU1
> [ 248.163960] ---- ----
> [ 248.168518] lock(xb_write_mutex);
> [ 248.172045] lock(&u->msgbuffer_mutex);
> [ 248.178500] lock(xb_write_mutex);
> [ 248.184514] lock(&u->msgbuffer_mutex);
> [ 248.188470]
> [ 248.188470] *** DEADLOCK ***
> [ 248.188470]
> [ 248.194578] 2 locks held by xenbus/91:
> [ 248.198360] #0: (xs_response_mutex){+.+...}, at:
> [<ffff00000863a7b0>] xenbus_thread+0x460/0x798
> [ 248.207218] #1: (xb_write_mutex){+.+...}, at: [<ffff00000863a940>]
> xenbus_thread+0x5f0/0x798
> [ 248.215818]
> [ 248.215818] stack backtrace:
> [ 248.220293] CPU: 0 PID: 91 Comm: xenbus Not tainted
> 4.12.0-rc4-00022-gc4b25c0 #575
> [ 248.227858] Hardware name: ARM Juno development board (r1) (DT)
> [ 248.233792] Call trace:
> [ 248.236289] [<ffff00000808a748>] dump_backtrace+0x0/0x270
> [ 248.241707] [<ffff00000808aa94>] show_stack+0x24/0x30
> [ 248.246782] [<ffff0000084caa98>] dump_stack+0xb8/0xf0
> [ 248.251859] [<ffff000008139068>] print_circular_bug+0x1f8/0x2e0
> [ 248.257787] [<ffff00000813c090>] __lock_acquire+0x1768/0x1778
> [ 248.263548] [<ffff00000813c90c>] lock_acquire+0xc4/0x288
> [ 248.268882] [<ffff000008bdb28c>] __mutex_lock+0x84/0x868
> [ 248.274219] [<ffff000008bdbaac>] mutex_lock_nested+0x3c/0x50
> [ 248.279889] [<ffff00000863e904>] xenbus_dev_queue_reply+0x3c/0x230
> [ 248.286081] [<ffff00000863aad8>] xenbus_thread+0x788/0x798
> [ 248.291585] [<ffff000008108070>] kthread+0x110/0x140
> [ 248.296572] [<ffff000008083710>] ret_from_fork+0x10/0x40
>
> Apparently it's not easily reproducible, but Julien confirmed that the
> dead lock condition as reported above is indeed in the Linux code.
>
> Does anyone has an idea of how to fix this?
Shouldn't be too hard. The xb_write_mutex can be dropped earlier in the
critical path. I'll send a patch.
Juergen
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Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel
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