[PATCH] md: clear MD_CLOSING when array_state_store() bails on interrupted lock

[Jack Wang <jinpu.wang@ionos.com>]

From: Jack Wang <jinpu.wang@cloud.ionos.com>

Writing "clear", "readonly", "inactive" or "read_auto" to array_state
calls mddev_set_closing_and_sync_blockdev(), which sets MD_CLOSING so the
array cannot be reopened while it is being torn down. The flag is only
cleared again at the tail of array_state_store() (for readonly, read_auto,
inactive, or the failed-clear case).

Between setting the flag and reaching that tail there is an early return:

	err = mddev_lock(mddev);
	if (err)
		return err;

mddev_lock() is mutex_lock_interruptible() on reconfig_mutex. If the
writing task is signalled while blocked there - easy to hit when the mutex
is held for a long time by a running resync/recovery or reshape - it
returns -EINTR and array_state_store() returns with MD_CLOSING still set.
do_md_stop()/md_set_readonly() never ran, so the array keeps working
internally, but every subsequent md_open() now returns -ENODEV for all
callers: the device still shows up in /proc/mdstat and sysfs is fully
populated, yet it cannot be opened and cannot be recovered without a
reboot (the remaining clear paths either need the device open or re-enter
test_and_set_bit(MD_CLOSING) and bail with -EBUSY before the clear).

Route the interrupted-lock exit through the existing MD_CLOSING clearing
logic instead of returning directly, mirroring the goto-out pattern
md_ioctl() already uses for the same flag. mddev_unlock() is correctly
skipped since the lock was never acquired.

Fixes: 99b902ac1725 ("md: sync blockdev before stopping raid or setting readonly")
Assisted-by: Claude:claude-opus-4-8 [Claude Code]
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
---
 drivers/md/md.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index d1465bcd86c8..c4de2053593a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4696,7 +4696,7 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
 	}
 	err = mddev_lock(mddev);
 	if (err)
-		return err;
+		goto out_clear_closing;
 
 	switch (st) {
 	case inactive:
@@ -4769,6 +4769,7 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len)
 	}
 	mddev_unlock(mddev);
 
+out_clear_closing:
 	if (st == readonly || st == read_auto || st == inactive ||
 	    (err && st == clear))
 		clear_bit(MD_CLOSING, &mddev->flags);
-- 
2.43.0