Commit dc868fb0 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi
Browse files

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: default avatarYongxue Hong <yhong@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarAlberto Garcia <berto@igalia.com>
Message-id: 20171110151934.16883-1-stefanha@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 632a7735

block/block-backend.c

+2 −0
Original line number Diff line number Diff line
@@ -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);

    }

block/throttle-groups.c

+6 −0
Original line number Diff line number Diff line
@@ -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;

}