block: always allocate genhd->ev if check_events is implemented

9fd097b149 (block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe drivers) removed DISK_EVENT_MEDIA_CHANGE from legacy/fringe block drivers which have inadequate ->check_events(). Combined with earlier change 7c88a168da (block: don't propagate unlisted DISK_EVENTs to userland), this enables using ->check_events() for internal processing while avoiding enabling in-kernel block event polling which can lead to infinite event loop.

Unfortunately, this made many drivers including floppy without any bit set in disk->events and ->async_events in which case disk_add_events() simply skipped allocation of disk->ev, which disables whole event handling. As ->check_events() is still used during open processing for revalidation, this can lead to open failure.

This patch always allocates disk->ev if ->check_events is implemented. In the long term, it would make sense to simply include the event structure inline into genhd as it's now used by virtually all block devices.

---
 block/genhd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 2dd9887..95822ae 100644
@@ -1728,7 +1728,7 @@ static void disk_add_events(struct gendisk *disk)
 {
 	struct disk_events *ev;
 
-	if (!disk->fops->check_events || !(disk->events | disk->async_events))
+	if (!disk->fops->check_events)
 		return;
 
 	ev = kzalloc(sizeof(*ev), GFP_KERNEL);

Thanks, applied.

Jens Axboe