Juergen Gross 1a3fc2c402 xen: avoid deadlock in xenbus driver ... There has been a report about a deadlock in the xenbus driver: [ 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 It is rather easy to avoid by dropping xb_write_mutex before calling xenbus_dev_queue_reply(). Fixes: fd8aa9095a ("xen: optimize xenbus driver for multiple concurrent xenstore accesses"). Cc: <stable@vger.kernel.org> # 4.11 Reported-by: Andre Przywara <andre.przywara@arm.com> Signed-off-by: Juergen Gross <jgross@suse.com> Tested-by: Andre Przywara <andre.przywara@arm.com> Signed-off-by: Juergen Gross <jgross@suse.com>		2017-06-25 13:11:22 +02:00
..
Makefile	xen: Add xenbus_backend device	2011-12-16 13:29:41 -05:00
xenbus.h	xen: optimize xenbus driver for multiple concurrent xenstore accesses	2017-02-09 11:26:49 -05:00
xenbus_client.c	xen: modify xenstore watch event interface	2017-02-09 11:26:49 -05:00
xenbus_comms.c	xen: avoid deadlock in xenbus driver	2017-06-25 13:11:22 +02:00
xenbus_dev_backend.c	xen: clean up xenbus internal headers	2017-02-09 11:26:49 -05:00
xenbus_dev_frontend.c	xenbus: remove transaction holder from list before freeing	2017-04-04 10:11:06 -04:00
xenbus_probe.c	xen: modify xenstore watch event interface	2017-02-09 11:26:49 -05:00
xenbus_probe_backend.c	xen: modify xenstore watch event interface	2017-02-09 11:26:49 -05:00
xenbus_probe_frontend.c	xen: modify xenstore watch event interface	2017-02-09 11:26:49 -05:00
xenbus_xs.c	xen: optimize xenbus driver for multiple concurrent xenstore accesses	2017-02-09 11:26:49 -05:00