[PATCH 2/2] loop: make autoclear operation synchronous again

[Christoph Hellwig <hch@xxxxxx>]

From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

The kernel test robot is reporting that xfstest can fail at

  umount ext2 on xfs
  umount xfs

sequence, for commit 322c4293ecc58110 ("loop: make autoclear operation
asynchronous") broke what commit ("loop: Make explicit loop device
destruction lazy") wanted to achieve.

Although we cannot guarantee that nobody is holding a reference when
"umount xfs" is called, we should try to close a race window opened
by asynchronous autoclear operation.

Make the autoclear operation upon close() synchronous, by performing
__loop_clr_fd() directly from the release callback.

Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Fixes: 322c4293ecc58110 ("loop: make autoclear operation asynchronous")
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
[hch: rebased]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 drivers/block/loop.c | 31 +------------------------------
 drivers/block/loop.h |  1 -
 2 files changed, 1 insertion(+), 31 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 573f0d83fe80a..7faacefc4ede9 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1156,40 +1156,12 @@ static void __loop_clr_fd(struct loop_device *lo)
 		lo->lo_disk->flags |= GENHD_FL_NO_PART;
 
 	fput(filp);
-}
-
-static void loop_rundown_completed(struct loop_device *lo)
-{
 	mutex_lock(&lo->lo_mutex);
 	lo->lo_state = Lo_unbound;
 	mutex_unlock(&lo->lo_mutex);
 	module_put(THIS_MODULE);
 }
 
-static void loop_rundown_workfn(struct work_struct *work)
-{
-	struct loop_device *lo = container_of(work, struct loop_device,
-					      rundown_work);
-	struct block_device *bdev = lo->lo_device;
-	struct gendisk *disk = lo->lo_disk;
-
-	__loop_clr_fd(lo);
-	kobject_put(&bdev->bd_device.kobj);
-	module_put(disk->fops->owner);
-	loop_rundown_completed(lo);
-}
-
-static void loop_schedule_rundown(struct loop_device *lo)
-{
-	struct block_device *bdev = lo->lo_device;
-	struct gendisk *disk = lo->lo_disk;
-
-	__module_get(disk->fops->owner);
-	kobject_get(&bdev->bd_device.kobj);
-	INIT_WORK(&lo->rundown_work, loop_rundown_workfn);
-	queue_work(system_long_wq, &lo->rundown_work);
-}
-
 static int loop_clr_fd(struct loop_device *lo)
 {
 	int err;
@@ -1220,7 +1192,6 @@ static int loop_clr_fd(struct loop_device *lo)
 	mutex_unlock(&lo->lo_mutex);
 
 	__loop_clr_fd(lo);
-	loop_rundown_completed(lo);
 	return 0;
 }
 
@@ -1745,7 +1716,7 @@ static void lo_release(struct gendisk *disk, fmode_t mode)
 		 * In autoclear mode, stop the loop thread
 		 * and remove configuration after last close.
 		 */
-		loop_schedule_rundown(lo);
+		__loop_clr_fd(lo);
 		return;
 	} else if (lo->lo_state == Lo_bound) {
 		/*
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 885c83b4417e1..0400cbfed6308 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -55,7 +55,6 @@ struct loop_device {
 	struct gendisk		*lo_disk;
 	struct mutex		lo_mutex;
 	bool			idr_visible;
-	struct work_struct      rundown_work;
 };
 
 struct loop_cmd {
-- 
2.30.2