fs: Drop wait_unfrozen wait queue

wait_unfrozen waitqueue is used only in quota code to wait for
filesystem to become unfrozen. In that place we can just use
sb_start_write() - sb_end_write() pair to achieve the same. So just
remove the waitqueue.

Reviewed-by: Christian Brauner <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/quota/quota.c

···
 			up_write(&sb->s_umount);
 		else
 			up_read(&sb->s_umount);
-		wait_event(sb->s_writers.wait_unfrozen,
-			   sb->s_writers.frozen == SB_UNFROZEN);
+		/* Wait for sb to unfreeze */
+		sb_start_write(sb);
+		sb_end_write(sb);
 		put_super(sb);
 		goto retry;
 	}

fs/super.c

···
 					&type->s_writers_key[i]))
 			goto fail;
 	}
-	init_waitqueue_head(&s->s_writers.wait_unfrozen);
 	s->s_bdi = &noop_backing_dev_info;
 	s->s_flags = flags;
 	if (s->s_user_ns != &init_user_ns)
···
 	if (ret) {
 		sb->s_writers.frozen = SB_UNFROZEN;
 		sb_freeze_unlock(sb, SB_FREEZE_PAGEFAULT);
-		wake_up(&sb->s_writers.wait_unfrozen);
 		deactivate_locked_super(sb);
 		return ret;
 	}
···
 				"VFS:Filesystem freeze failed\n");
 			sb->s_writers.frozen = SB_UNFROZEN;
 			sb_freeze_unlock(sb, SB_FREEZE_FS);
-			wake_up(&sb->s_writers.wait_unfrozen);
 			deactivate_locked_super(sb);
 			return ret;
 		}
···
 	sb->s_writers.frozen = SB_UNFROZEN;
 	sb_freeze_unlock(sb, SB_FREEZE_FS);
 out:
-	wake_up(&sb->s_writers.wait_unfrozen);
 	deactivate_locked_super(sb);
 	return 0;
 }

include/linux/fs.h

···
 
 struct sb_writers {
 	int				frozen;		/* Is sb frozen? */
-	wait_queue_head_t		wait_unfrozen;	/* wait for thaw */
 	struct percpu_rw_semaphore	rw_sem[SB_FREEZE_LEVELS];
 };