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From 9e1beaad709ba68a82a54738ad7b50cac69861cc Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Fri, 17 Nov 2017 11:19:04 +0100
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Subject: [PATCH 05/15] throttle-groups: drain before detaching ThrottleState
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RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
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Message-id: <20171117111908.8815-6-stefanha@redhat.com>
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Patchwork-id: 77740
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O-Subject: [RHV7.5 qemu-kvm-rhev PATCH 5/9] throttle-groups: drain before detaching ThrottleState
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Bugzilla: 1492295
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RH-Acked-by: John Snow <jsnow@redhat.com>
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RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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I/O requests hang after stop/cont commands at least since QEMU 2.10.0
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with -drive iops=100:
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(guest)$ dd if=/dev/zero of=/dev/vdb oflag=direct count=1000
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(qemu) stop
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(qemu) cont
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...I/O is stuck...
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This happens because blk_set_aio_context() detaches the ThrottleState
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while requests may still be in flight:
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if (tgm->throttle_state) {
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throttle_group_detach_aio_context(tgm);
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throttle_group_attach_aio_context(tgm, new_context);
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}
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This patch encloses the detach/attach calls in a drained region so no
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I/O request is left hanging. Also add assertions so we don't make the
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same mistake again in the future.
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Reported-by: Yongxue Hong <yhong@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Reviewed-by: Alberto Garcia <berto@igalia.com>
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Message-id: 20171110151934.16883-1-stefanha@redhat.com
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit dc868fb03b9b829ed9d2ecdae0fcc12f3fe19b4f)
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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block/block-backend.c | 2 ++
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block/throttle-groups.c | 6 ++++++
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2 files changed, 8 insertions(+)
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diff --git a/block/block-backend.c b/block/block-backend.c
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index bfb3e84..520f2b2 100644
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--- a/block/block-backend.c
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+++ b/block/block-backend.c
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@@ -1771,8 +1771,10 @@ void blk_set_aio_context(BlockBackend *blk, AioContext *new_context)
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if (bs) {
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if (tgm->throttle_state) {
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+ bdrv_drained_begin(bs);
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throttle_group_detach_aio_context(tgm);
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throttle_group_attach_aio_context(tgm, new_context);
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+ bdrv_drained_end(bs);
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}
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bdrv_set_aio_context(bs, new_context);
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}
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diff --git a/block/throttle-groups.c b/block/throttle-groups.c
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index 7749cf0..44cc1e6 100644
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--- a/block/throttle-groups.c
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+++ b/block/throttle-groups.c
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@@ -568,6 +568,12 @@ void throttle_group_attach_aio_context(ThrottleGroupMember *tgm,
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void throttle_group_detach_aio_context(ThrottleGroupMember *tgm)
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{
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ThrottleTimers *tt = &tgm->throttle_timers;
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+
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+ /* Requests must have been drained */
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+ assert(tgm->pending_reqs[0] == 0 && tgm->pending_reqs[1] == 0);
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+ assert(qemu_co_queue_empty(&tgm->throttled_reqs[0]));
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+ assert(qemu_co_queue_empty(&tgm->throttled_reqs[1]));
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+
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throttle_timers_detach_aio_context(tt);
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tgm->aio_context = NULL;
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}
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--
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1.8.3.1
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