[PATCH v4 1/2] mtd: spi-nor: core: Fix mutex leak in spi_nor_rww_start_exclusive()

[Runyu Xiao]

The RWW wait helpers must not block while evaluating the condition.
spi_nor_rww_start_exclusive() used mutex_lock() directly and could return
with nor->lock still held.

Switch the four RWW start helpers to conditional scoped mutex guards so
the wait condition never sleeps and nor->lock is released before return.

Fixes: 74df43b3f626 ("mtd: spi-nor: Enhance locking to support reads while writes")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Runyu Xiao <runyu.xiao@xxxxxxxxxx>

Changes in v4:
- Use the original RWW locking commit in Fixes and update the subject.
- Apply the locking fix to all RWW start helpers used as wait conditions.
- Keep commit 03e7bb864d9a ("mtd: spi-nor: use scope-based mutex
  cleanup helpers") as a stable prerequisite because it adds cleanup.h.
---
 drivers/mtd/spi-nor/core.c | 84 ++++++++++++++++++++------------------
 1 file changed, 45 insertions(+), 39 deletions(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index ccf4396cdcd0..d5c6a925862e 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -1273,14 +1273,15 @@ static bool spi_nor_rww_start_io(struct spi_nor *nor)
 {
 	struct spi_nor_rww *rww = &nor->rww;
 
-	guard(mutex)(&nor->lock);
-
-	if (rww->ongoing_io)
-		return false;
+	scoped_guard(mutex_try, &nor->lock) {
+		if (rww->ongoing_io)
+			return false;
 
-	rww->ongoing_io = true;
+		rww->ongoing_io = true;
+		return true;
+	}
 
-	return true;
+	return false;
 }
 
 static void spi_nor_rww_end_io(struct spi_nor *nor)
@@ -1310,16 +1311,17 @@ static bool spi_nor_rww_start_exclusive(struct spi_nor *nor)
 {
 	struct spi_nor_rww *rww = &nor->rww;
 
-	mutex_lock(&nor->lock);
-
-	if (rww->ongoing_io || rww->ongoing_rd || rww->ongoing_pe)
-		return false;
+	scoped_guard(mutex_try, &nor->lock) {
+		if (rww->ongoing_io || rww->ongoing_rd || rww->ongoing_pe)
+			return false;
 
-	rww->ongoing_io = true;
-	rww->ongoing_rd = true;
-	rww->ongoing_pe = true;
+		rww->ongoing_io = true;
+		rww->ongoing_rd = true;
+		rww->ongoing_pe = true;
+		return true;
+	}
 
-	return true;
+	return false;
 }
 
 static void spi_nor_rww_end_exclusive(struct spi_nor *nor)
@@ -1369,23 +1371,25 @@ static bool spi_nor_rww_start_pe(struct spi_nor *nor, loff_t start, size_t len)
 	u8 first, last;
 	int bank;
 
-	guard(mutex)(&nor->lock);
+	scoped_guard(mutex_try, &nor->lock) {
+		if (rww->ongoing_io || rww->ongoing_rd || rww->ongoing_pe)
+			return false;
 
-	if (rww->ongoing_io || rww->ongoing_rd || rww->ongoing_pe)
-		return false;
+		spi_nor_offset_to_banks(nor->params->bank_size, start, len,
+					&first, &last);
+		for (bank = first; bank <= last; bank++) {
+			if (rww->used_banks & BIT(bank))
+				return false;
 
-	spi_nor_offset_to_banks(nor->params->bank_size, start, len, &first, &last);
-	for (bank = first; bank <= last; bank++) {
-		if (rww->used_banks & BIT(bank))
-			return false;
+			used_banks |= BIT(bank);
+		}
 
-		used_banks |= BIT(bank);
+		rww->used_banks |= used_banks;
+		rww->ongoing_pe = true;
+		return true;
 	}
 
-	rww->used_banks |= used_banks;
-	rww->ongoing_pe = true;
-
-	return true;
+	return false;
 }
 
 static void spi_nor_rww_end_pe(struct spi_nor *nor, loff_t start, size_t len)
@@ -1440,24 +1444,26 @@ static bool spi_nor_rww_start_rd(struct spi_nor *nor, loff_t start, size_t len)
 	u8 first, last;
 	int bank;
 
-	guard(mutex)(&nor->lock);
+	scoped_guard(mutex_try, &nor->lock) {
+		if (rww->ongoing_io || rww->ongoing_rd)
+			return false;
 
-	if (rww->ongoing_io || rww->ongoing_rd)
-		return false;
+		spi_nor_offset_to_banks(nor->params->bank_size, start, len,
+					&first, &last);
+		for (bank = first; bank <= last; bank++) {
+			if (rww->used_banks & BIT(bank))
+				return false;
 
-	spi_nor_offset_to_banks(nor->params->bank_size, start, len, &first, &last);
-	for (bank = first; bank <= last; bank++) {
-		if (rww->used_banks & BIT(bank))
-			return false;
+			used_banks |= BIT(bank);
+		}
 
-		used_banks |= BIT(bank);
+		rww->used_banks |= used_banks;
+		rww->ongoing_io = true;
+		rww->ongoing_rd = true;
+		return true;
 	}
 
-	rww->used_banks |= used_banks;
-	rww->ongoing_io = true;
-	rww->ongoing_rd = true;
-
-	return true;
+	return false;
 }
 
 static void spi_nor_rww_end_rd(struct spi_nor *nor, loff_t start, size_t len)
-- 
2.34.1