[PATCH v5] mtd: spi-nor: core: Fix mutex leak in spi_nor_rww_start_exclusive()

[Runyu Xiao]

spi_nor_rww_start_exclusive() is used as a wait_event_killable()
condition. When an RWW operation is already in progress, it returns
false while still holding nor->lock. The wait condition is then retried,
but spi_nor_rww_end_exclusive() needs the same lock to clear the RWW
state, so the wait can deadlock.

Use the same guard(mutex) pattern as the other RWW helpers so nor->lock
is released on both the busy and successful return paths.

Fixes: 03e7bb864d9a ("mtd: spi-nor: use scope-based mutex cleanup helpers")
Cc: stable at vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao at seu.edu.cn>
---
Changes in v5:
- Drop the interrupted-wait cleanup patch because an equivalent fix is
  already pending upstream.
- Restore the focused guard(mutex) change for the exclusive RWW helper.
- Restore the original Fixes tag and keep the other RWW helpers unchanged.

Changes in v4:
- Add the interrupted-wait cleanup as a separate patch.
- Convert all RWW start helpers used as wait conditions to conditional
  scoped mutex guards.
- Update the subject and change the Fixes tag while reworking the patch.

Changes in v3:
- Use guard(mutex) in spi_nor_rww_start_exclusive() so the lock is
  released on both return paths.
- Update the subject to describe the guard-based fix.

Changes in v2:
- Explicitly unlock nor->lock before returning from the busy path.
- Clarify the lock leak and its effect on the matching end helper.

 drivers/mtd/spi-nor/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index ccf4396cdcd0..8bc117b46e02 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -1310,7 +1310,7 @@ static bool spi_nor_rww_start_exclusive(struct spi_nor *nor)
 {
 	struct spi_nor_rww *rww = &nor->rww;
 
-	mutex_lock(&nor->lock);
+	guard(mutex)(&nor->lock);
 
 	if (rww->ongoing_io || rww->ongoing_rd || rww->ongoing_pe)
 		return false;
-- 
2.34.1