The mddev data structure is freed in mddev_delayed_delete(), which is
schedualed after the array is deconfigured completely when stopping. So
there is a race window between md_open() and do_md_stop(), which leads
to /dev/mdX can still be opened by userspace even it's not accessible
any more. As a result, a DeviceDisappeared event will not be able to be
monitored by mdadm in monitor mode. This patch tries to fix it by adding
this new flag MD_DELETING.

Signed-off-by: Lidong Zhong <redacted>
---
 drivers/md/md.c | 4 +++-
 drivers/md/md.h | 2 ++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 21da0c48f6c2..566df2491318 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -6439,6 +6439,7 @@ static int do_md_stop(struct mddev *mddev, int mode,
 		md_clean(mddev);
 		if (mddev->hold_active == UNTIL_STOP)
 			mddev->hold_active = 0;
+		set_bit(MD_DELETING, &mddev->flags);
 	}
 	md_new_event(mddev);
 	sysfs_notify_dirent_safe(mddev->sysfs_state);

@@ -7829,7 +7830,8 @@ static int md_open(struct block_device *bdev, fmode_t mode)
 	if ((err = mutex_lock_interruptible(&mddev->open_mutex)))
 		goto out;
 
-	if (test_bit(MD_CLOSING, &mddev->flags)) {
+	if (test_bit(MD_CLOSING, &mddev->flags) ||
+            (test_bit(MD_DELETING, &mddev->flags) && mddev->pers == NULL)) {
 		mutex_unlock(&mddev->open_mutex);
 		err = -ENODEV;
 		goto out;

diff --git a/drivers/md/md.h b/drivers/md/md.h
index bcbba1b5ec4a..83c7aa61699f 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h

@@ -262,6 +262,8 @@ enum mddev_flags {
 	MD_BROKEN,              /* This is used in RAID-0/LINEAR only, to stop
 				 * I/O in case an array member is gone/failed.
 				 */
+	MD_DELETING,		/* If set, we are deleting the array, do not open
+				 * it then */
 };
 
 enum mddev_sb_flags {