From ae4ca7d9cfb0033cf39971f1c59e9a20a80c9bee Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Fri, 17 Nov 2017 11:19:08 +0100
Subject: [PATCH 09/15] throttle-groups: forget timer and schedule next TGM on
 detach

RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: <20171117111908.8815-10-stefanha@redhat.com>
Patchwork-id: 77744
O-Subject: [RHV7.5 qemu-kvm-rhev PATCH 9/9] throttle-groups: forget timer and schedule next TGM on detach
Bugzilla: 1492295
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
RH-Acked-by: Thomas Huth <thuth@redhat.com>

tg->any_timer_armed[] must be cleared when detaching pending timers from
the AioContext.  Failure to do so leads to hung I/O because it looks
like there are still timers pending when in fact they have been removed.

Other ThrottleGroupMembers might have requests pending too so it's
necessary to schedule the next TGM so it can set a timer.

This patch fixes hung I/O when QEMU is launched with drives that are in
the same throttling group:

  (guest)$ dd if=/dev/zero of=/dev/vdb oflag=direct bs=512 &
  (guest)$ dd if=/dev/zero of=/dev/vdc oflag=direct bs=512 &
  (qemu) stop
  (qemu) cont
  ...I/O is stuck...

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20171116112150.27607-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit 341e0b5658681f46680024cdbfc998717d85cc35)
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block/throttle-groups.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/block/throttle-groups.c b/block/throttle-groups.c
index 44cc1e6..35c22ac 100644
--- a/block/throttle-groups.c
+++ b/block/throttle-groups.c
@@ -567,13 +567,25 @@ void throttle_group_attach_aio_context(ThrottleGroupMember *tgm,
 
 void throttle_group_detach_aio_context(ThrottleGroupMember *tgm)
 {
+    ThrottleGroup *tg = container_of(tgm->throttle_state, ThrottleGroup, ts);
     ThrottleTimers *tt = &tgm->throttle_timers;
+    int i;
 
     /* 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]));
 
+    /* Kick off next ThrottleGroupMember, if necessary */
+    qemu_mutex_lock(&tg->lock);
+    for (i = 0; i < 2; i++) {
+        if (timer_pending(tt->timers[i])) {
+            tg->any_timer_armed[i] = false;
+            schedule_next_request(tgm, i);
+        }
+    }
+    qemu_mutex_unlock(&tg->lock);
+
     throttle_timers_detach_aio_context(tt);
     tgm->aio_context = NULL;
 }
-- 
1.8.3.1