From: Juergen Gross <jgross@suse.com>
To: Andre Przywara <andre.przywara@arm.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Julien Grall <julien.grall@arm.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: Xen Linux deadlock
Date: Wed, 7 Jun 2017 17:51:58 +0200 [thread overview]
Message-ID: <029a288a-2e80-5eae-202c-9eb166055e87@suse.com> (raw)
In-Reply-To: <22b46162-435c-d971-5fa7-684c71950a62@arm.com>
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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prev parent reply other threads:[~2017-06-07 15:52 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-07 15:05 Xen Linux deadlock Andre Przywara
2017-06-07 15:51 ` Juergen Gross [this message]
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