From dc868fb03b9b829ed9d2ecdae0fcc12f3fe19b4f Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Fri, 10 Nov 2017 15:19:34 +0000 Subject: throttle-groups: drain before detaching ThrottleState 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 Signed-off-by: Stefan Hajnoczi Reviewed-by: Alberto Garcia Message-id: 20171110151934.16883-1-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi --- 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 18e543780d..ab75da32c9 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -1752,8 +1752,10 @@ 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; } -- cgit v1.2.3