[PATCH v3] mtd: spi-nor: use guard() in spi_nor_rww_start_exclusive

[Runyu Xiao]

Commit 03e7bb864d9a ("mtd: spi-nor: use scope-based mutex cleanup
helpers") converted the RWW start helpers to scoped mutex cleanup, but
left spi_nor_rww_start_exclusive() using a plain mutex_lock().

spi_nor_rww_start_exclusive() is used as a wait_event_killable()
condition. When it returns false on the busy path, the raw mutex_lock()
leaves nor->lock held and blocks the operation that must clear the RWW
state in spi_nor_rww_end_exclusive().

Use guard(mutex) here as well so this helper matches the other RWW
start helpers and releases nor->lock on the false return path.

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 v3:
- Reframe the changelog around the scoped-helper conversion that missed
  spi_nor_rww_start_exclusive().

Changes in v2:
- Replace the analysis-style explanation with a short maintainer-facing
  description of the busy-path lock hold.
- Keep the fix focused on using guard(mutex) so the mutex is released on
  both paths.

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