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test-bdrv-drain: fix iothread_join() hang

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tests/test-bdrv-drain can hang in tests/iothread.c:iothread_run():

  while (!atomic_read(&iothread->stopping)) {
      aio_poll(iothread->ctx, true);
  }

The iothread_join() function works as follows:

  void iothread_join(IOThread *iothread)
  {
      iothread->stopping = true;
      aio_notify(iothread->ctx);
      qemu_thread_join(&iothread->thread);

If iothread_run() checks iothread->stopping before the iothread_join()
thread sets stopping to true, then aio_notify() may be optimized away
and iothread_run() hangs forever in aio_poll().

The correct way to change iothread->stopping is from a BH that executes
within iothread_run().  This ensures that iothread->stopping is checked
after we set it to true.

This was already fixed for ./iothread.c (note this is a different source
file!) by commit 2362a28ea1 ("iothread:
fix iothread_stop() race condition"), but not for tests/iothread.c.

Fixes: 0c330a734b
       ("aio: introduce aio_co_schedule and aio_co_wake")
Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20191003100103.331-1-stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2019-10-03 11:01:03 +01:00
parent 98b2e3c9ab
commit 69de48445a
1 changed files with 8 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

10
tests/iothread.c
View file

@ -55,10 +55,16 @@ static void *iothread_run(void *opaque)
return NULL;
}
static void iothread_stop_bh(void *opaque)
{
IOThread *iothread = opaque;
iothread->stopping = true;
}
void iothread_join(IOThread *iothread)
{
iothread->stopping = true;
aio_notify(iothread->ctx);
aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
qemu_thread_join(&iothread->thread);
qemu_cond_destroy(&iothread->init_done_cond);
qemu_mutex_destroy(&iothread->init_done_lock);