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[Qemu-block] [PATCH] virtio-blk: dataplane: release AioContext before bl
From: |
Sergio Lopez |
Subject: |
[Qemu-block] [PATCH] virtio-blk: dataplane: release AioContext before blk_set_aio_context |
Date: |
Wed, 27 Feb 2019 17:52:12 +0100 |
Stopping the dataplane requires calling to blk_set_aio_context, which
may need to wait for a running job to be completed or paused.
As stopping the dataplane is something that can be triggered from a vcpu
thread (due to the Guest requesting to stop the device), while the job
itself may be managed by an iothread, holding the AioContext will lead
to a deadlock, where the first one is waiting for the job to pause or
finish, while the second can't make any progress as it's waiting for the
AioContext to be released:
Thread 6 (LWP 90472)
#0 0x000055a6f8497aee in blk_root_drained_end
#1 0x000055a6f84a7926 in bdrv_parent_drained_end
#2 0x000055a6f84a799f in bdrv_do_drained_end
#3 0x000055a6f84a82ab in bdrv_drained_end
#4 0x000055a6f8498be8 in blk_drain
#5 0x000055a6f84a22cd in mirror_drain
#6 0x000055a6f8457708 in block_job_detach_aio_context
#7 0x000055a6f84538f1 in bdrv_detach_aio_context
#8 0x000055a6f8453a96 in bdrv_set_aio_context
#9 0x000055a6f84999f8 in blk_set_aio_context
#10 0x000055a6f81802c8 in virtio_blk_data_plane_stop
#11 0x000055a6f83cfc95 in virtio_bus_stop_ioeventfd
#12 0x000055a6f83d1f81 in virtio_pci_common_write
#13 0x000055a6f83d1f81 in virtio_pci_common_write
#14 0x000055a6f8148d62 in memory_region_write_accessor
#15 0x000055a6f81459c9 in access_with_adjusted_size
#16 0x000055a6f814a608 in memory_region_dispatch_write
#17 0x000055a6f80f1f98 in flatview_write_continue
#18 0x000055a6f80f214f in flatview_write
#19 0x000055a6f80f6a7b in address_space_write
#20 0x000055a6f80f6b15 in address_space_rw
#21 0x000055a6f815da08 in kvm_cpu_exec
#22 0x000055a6f8132fee in qemu_kvm_cpu_thread_fn
#23 0x000055a6f8551306 in qemu_thread_start
#24 0x00007f9bdf5b9dd5 in start_thread
#25 0x00007f9bdf2e2ead in clone
Thread 8 (LWP 90467)
#0 0x00007f9bdf5c04ed in __lll_lock_wait
#1 0x00007f9bdf5bbde6 in _L_lock_941
#2 0x00007f9bdf5bbcdf in __GI___pthread_mutex_lock
#3 0x000055a6f8551447 in qemu_mutex_lock_impl
#4 0x000055a6f854be77 in co_schedule_bh_cb
#5 0x000055a6f854b781 in aio_bh_poll
#6 0x000055a6f854b781 in aio_bh_poll
#7 0x000055a6f854f01b in aio_poll
#8 0x000055a6f825a488 in iothread_run
#9 0x000055a6f8551306 in qemu_thread_start
#10 0x00007f9bdf5b9dd5 in start_thread
#11 0x00007f9bdf2e2ead in clone
(gdb) thread 8
[Switching to thread 8 (Thread 0x7f9bd6dae700 (LWP 90467))]
#3 0x000055a6f8551447 in qemu_mutex_lock_impl (mutex=0x55a6fac8fea0,
file=0x55a6f8730c3f "util/async.c", line=511) at
util/qemu-thread-posix.c:66
66 err = pthread_mutex_lock(&mutex->lock);
(gdb) up 3
#3 0x000055a6f8551447 in qemu_mutex_lock_impl (mutex=0x55a6fac8fea0,
file=0x55a6f8730c3f "util/async.c", line=511) at
util/qemu-thread-posix.c:66
66 err = pthread_mutex_lock(&mutex->lock);
(gdb) p mutex.lock.__data.__owner
$6 = 90472
Signed-off-by: Sergio Lopez <address@hidden>
---
hw/block/dataplane/virtio-blk.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 8c37bd314a..358e6ae89b 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -280,12 +280,11 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
aio_context_acquire(s->ctx);
aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
+ aio_context_release(s->ctx);
/* Drain and switch bs back to the QEMU main loop */
blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context());
- aio_context_release(s->ctx);
-
for (i = 0; i < nvqs; i++) {
virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
--
2.20.1
- [Qemu-block] [PATCH] virtio-blk: dataplane: release AioContext before blk_set_aio_context,
Sergio Lopez <=