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1a3fc2c402
linux/drivers/xen
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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
..
events xen-evtchn: Bind dyn evtchn:qemu-dm interrupt to next online VCPU 2017-06-13 15:30:27 +02:00
xen-pciback xen: modify xenstore watch event interface 2017-02-09 11:26:49 -05:00
xenbus xen: avoid deadlock in xenbus driver 2017-06-25 13:11:22 +02:00
xenfs fs: constify tree_descr arrays passed to simple_fill_super() 2017-04-26 23:54:06 -04:00
acpi.c xen: rename dom0_op to platform_op 2015-12-21 14:40:55 +00:00
arm-device.c Xen: ARM: Zero reserved fields of xatp before making hypervisor call 2017-01-03 10:06:13 -08:00
balloon.c xen/balloon: decorate PV-only parts with #ifdef CONFIG_XEN_PV 2017-05-02 11:09:56 +02:00
biomerge.c xen/biomerge: Don't allow biovec's to be merged when Linux is not using 4KB pages 2015-10-23 14:20:36 +01:00
cpu_hotplug.c xen: modify xenstore watch event interface 2017-02-09 11:26:49 -05:00
dbgp.c
efi.c xen: Implement EFI reset_system callback 2017-05-02 12:06:50 +02:00
evtchn.c xen-evtchn: Bind dyn evtchn:qemu-dm interrupt to next online VCPU 2017-06-13 15:30:27 +02:00
fallback.c
features.c xen: audit usages of module.h ; remove unnecessary instances 2016-03-21 15:13:32 +00:00
gntalloc.c xen: set error code on failures 2016-12-08 07:53:50 +01:00
gntdev.c drivers, xen: convert grant_map.users from atomic_t to refcount_t 2017-03-13 12:45:18 -04:00
grant-table.c xen/pvh: Initialize grant table for PVH guests 2017-02-07 08:07:01 -05:00
Kconfig ARM64: XEN: Add a function to initialize Xen specific UEFI runtime services 2016-07-06 10:34:46 +01:00
Makefile Xen: ARM: Add support for mapping platform device mmio 2016-07-06 10:34:43 +01:00
manage.c xen: don't print error message in case of missing Xenstore entry 2017-06-07 09:48:02 +02:00
mcelog.c
pci.c xen/pci: Try harder to get PXM information for Xen 2015-04-15 10:57:28 +01:00
pcpu.c xen: rename dom0_op to platform_op 2015-12-21 14:40:55 +00:00
platform-pci.c xen: Revert commits da72ff5bfc and 72a9b18629 2017-05-02 11:18:05 +02:00
preempt.c xen/preempt: use need_resched() instead of should_resched() 2015-08-20 12:24:14 +01:00
privcmd.c mm, fs: reduce fault, page_mkwrite, and pfn_mkwrite to take only vmf 2017-02-24 17:46:54 -08:00
privcmd.h
swiotlb-xen.c xen/arm,arm64: rename __generic_dma_ops to xen_get_dma_ops 2017-05-02 11:14:47 +02:00
sys-hypervisor.c xen: add sysfs node for hypervisor build id 2017-06-15 08:50:37 +02:00
time.c xen: add static initialization of steal_clock op to xen_time_ops 2016-07-26 14:07:06 +01:00
tmem.c cleancache: constify cleancache_ops structure 2016-01-27 09:09:57 -05:00
xen-acpi-cpuhotplug.c xen: rename dom0_op to platform_op 2015-12-21 14:40:55 +00:00
xen-acpi-memhotplug.c
xen-acpi-pad.c xen: rename dom0_op to platform_op 2015-12-21 14:40:55 +00:00
xen-acpi-processor.c xen/acpi: upload PM state from init-domain to Xen 2017-03-23 12:00:02 -04:00
xen-balloon.c xen: modify xenstore watch event interface 2017-02-09 11:26:49 -05:00
xen-scsiback.c target: make close_session optional 2016-05-10 01:19:26 -07:00
xen-selfballoon.c mm, frontswap: convert frontswap_enabled to static key 2016-07-26 16:19:19 -07:00
xen-stub.c
xlate_mmu.c Xen: xlate: Use page_to_xen_pfn instead of page_to_pfn 2016-07-06 10:34:42 +01:00