md: Wait for md_check_recovery before attempting device removal.

When a device has failed, it needs to be removed from the personality
module before it can be removed from the array as a whole.
The first step is performed by md_check_recovery() which is called
from the raid management thread.

So when a HOT_REMOVE ioctl arrives, wait briefly for md_check_recovery
to have run.  This increases the chance that the ioctl will succeed.
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Neil Brown <nfbrown@suse.de>

drivers/md/md.c

@@ -6405,6 +6405,12 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
 		/* need to ensure md_delayed_delete() has completed */
 		flush_workqueue(md_misc_wq);
 
+	if (cmd == HOT_REMOVE_DISK)
+		/* need to ensure recovery thread has run */
+		wait_event_interruptible_timeout(mddev->sb_wait,
+						 !test_bit(MD_RECOVERY_NEEDED,
+							   &mddev->flags),
+						 msecs_to_jiffies(5000));
 	err = mddev_lock(mddev);
 	if (err) {
 		printk(KERN_INFO 
@@ -7892,6 +7898,8 @@ void md_check_recovery(struct mddev *mddev)
 			md_new_event(mddev);
 		}
 	unlock:
+		wake_up(&mddev->sb_wait);
+
 		if (!mddev->sync_thread) {
 			clear_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
 			if (test_and_clear_bit(MD_RECOVERY_RECOVER,