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[Qemu-block] [PATCH v4] throttle-groups: drain before detaching Throttle
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-block] [PATCH v4] throttle-groups: drain before detaching ThrottleState |
Date: |
Fri, 10 Nov 2017 15:19:34 +0000 |
I/O requests hang after stop/cont commands at least since QEMU 2.10.0
with -drive iops=100:
(guest)$ dd if=/dev/zero of=/dev/vdb oflag=direct count=1000
(qemu) stop
(qemu) cont
...I/O is stuck...
This happens because blk_set_aio_context() detaches the ThrottleState
while requests may still be in flight:
if (tgm->throttle_state) {
throttle_group_detach_aio_context(tgm);
throttle_group_attach_aio_context(tgm, new_context);
}
This patch encloses the detach/attach calls in a drained region so no
I/O request is left hanging. Also add assertions so we don't make the
same mistake again in the future.
Reported-by: Yongxue Hong <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
v4:
* Simplified patch in response to Berto's review
---
block/block-backend.c | 2 ++
block/throttle-groups.c | 6 ++++++
2 files changed, 8 insertions(+)
diff --git a/block/block-backend.c b/block/block-backend.c
index 45d9101be3..da2f6c0f8a 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1748,8 +1748,10 @@ void blk_set_aio_context(BlockBackend *blk, AioContext
*new_context)
if (bs) {
if (tgm->throttle_state) {
+ bdrv_drained_begin(bs);
throttle_group_detach_aio_context(tgm);
throttle_group_attach_aio_context(tgm, new_context);
+ bdrv_drained_end(bs);
}
bdrv_set_aio_context(bs, new_context);
}
diff --git a/block/throttle-groups.c b/block/throttle-groups.c
index b291a88481..2587f19ca3 100644
--- a/block/throttle-groups.c
+++ b/block/throttle-groups.c
@@ -594,6 +594,12 @@ void throttle_group_attach_aio_context(ThrottleGroupMember
*tgm,
void throttle_group_detach_aio_context(ThrottleGroupMember *tgm)
{
ThrottleTimers *tt = &tgm->throttle_timers;
+
+ /* Requests must have been drained */
+ assert(tgm->pending_reqs[0] == 0 && tgm->pending_reqs[1] == 0);
+ assert(qemu_co_queue_empty(&tgm->throttled_reqs[0]));
+ assert(qemu_co_queue_empty(&tgm->throttled_reqs[1]));
+
throttle_timers_detach_aio_context(tt);
tgm->aio_context = NULL;
}
--
2.13.6
- [Qemu-block] [PATCH v4] throttle-groups: drain before detaching ThrottleState,
Stefan Hajnoczi <=