Hello,

On Mon, Oct 29, 2012 at 05:01:36PM +0800, Aaron Lu wrote:

ODD_suspend                        disk_events_workfn
  ata_port_suspend                   check_events
    disk_block_events                  resume ODD
      cancel_delayed_work_sync           resume parent
      (waiting for disk_events_workfn)   (waiting for suspend callback)

I don't understand why solving it needs to be this elaborate.
check_event() can retry.  Just add a per-sr mutex which is try-locked
by sr_block_check_events() and grab it when entering zero power.

+/*
+ * Under some circumstances, there is a race between the calling thread
+ * of disk_block_events and the events checking function. To avoid such a race,
+ * this function will check if the delayed work is pending. If not, it means
+ * the work is either not queued or is already running, false is returned.
+ * And if yes, try to cancel the delayed work. If succedded, disk_block_events
+ * will be called and there is no worry that cancel_delayed_work_sync will
+ * deadlock the events checking function. And if failed, false is returned.
+ */
+bool disk_try_block_events(struct gendisk *disk)
+{
+	struct disk_events *ev = disk->ev;
+
+	if (!ev)
+		return false;
+
+	if (delayed_work_pending(&ev->dwork)) {

And please don't use delayed_work_pending() like this.  It doesn't add
anything.  cancel_delayed_work() already needs to perform all the
necessary tests.

+		if (cancel_delayed_work(&disk->ev->dwork)) {
+			disk_block_events(disk);
+			return true;
+		}
+	}
+
+	return false;
+}

Thanks.

-- 
tejun