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[PULL,for-2.11,1/1] throttle-groups: forget timer and schedule next TGM on detach

Message ID 20171116163614.24710-2-stefanha@redhat.com
State New
Headers show
Series [PULL,for-2.11,1/1] throttle-groups: forget timer and schedule next TGM on detach | expand

Commit Message

Stefan Hajnoczi Nov. 16, 2017, 4:36 p.m. UTC 
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>
---
 block/throttle-groups.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)
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Patch

diff --git a/block/throttle-groups.c b/block/throttle-groups.c
index 2587f19ca3..f26bcb5eee 100644
--- a/block/throttle-groups.c
+++ b/block/throttle-groups.c
@@ -593,13 +593,25 @@  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;
 }