[PATCH 0/2] Add lockdep_assert_not_held()

Some kernel functions must not be called holding a specific lock. Doing
so could lead to locking problems. Currently these routines call
lock_is_held() to check for lock hold followed by WARN_ON.

Adding a common lockdep interface will help reduce the duplication of this
logic in the rest of the kernel.

Add lockdep_assert_not_held() to be used in these functions to detect
incorrect calls while holding a lock.

lockdep_assert_not_held() provides the opposite functionality of
lockdep_assert_held() which is used to assert calls that require
holding a specific lock.

The need for lockdep_assert_not_held() came up in a discussion on
ath10k patch. ath10k_drain_tx() and i915_vma_pin_ww() are examples
of functions that can use lockdep_assert_not_held().

Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/

This patch series adds lockdep_assert_not_held() and uses it in the
second patch in ath10k_drain_tx() function.

Shuah Khan (2):
  lockdep: add lockdep_assert_not_held()
  ath10k: detect conf_mutex held ath10k_drain_tx() calls

 drivers/net/wireless/ath/ath10k/mac.c | 2 ++
 include/linux/lockdep.h               | 7 ++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

-- 
2.27.0

Some kernel functions must not be called holding a specific lock. Doing
so could lead to locking problems. Currently these routines call
lock_is_held() to check for lock hold followed by WARN_ON.

Adding a common lockdep interface will help reduce the duplication of this
logic in the rest of the kernel.

Add lockdep_assert_not_held() to be used in these functions to detect
incorrect calls while holding a lock.

lockdep_assert_not_held() provides the opposite functionality of
lockdep_assert_held() which is used to assert calls that require
holding a specific lock.

The need for lockdep_assert_not_held() came up in a discussion on
ath10k patch. ath10k_drain_tx() and i915_vma_pin_ww() are examples
of functions that can use lockdep_assert_not_held().

Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
---
 include/linux/lockdep.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..567e3a1a27ce 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h

@@ -294,6 +294,10 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
 
 #define lockdep_depth(tsk)	(debug_locks ? (tsk)->lockdep_depth : 0)
 
+#define lockdep_assert_not_held(l)	do {			\
+		WARN_ON(debug_locks && lockdep_is_held(l));	\
+	} while (0)
+
 #define lockdep_assert_held(l)	do {				\
 		WARN_ON(debug_locks && !lockdep_is_held(l));	\
 	} while (0)

@@ -383,8 +387,9 @@ extern int lock_is_held(const void *);
 extern int lockdep_is_held(const void *);
 #define lockdep_is_held_type(l, r)		(1)
 
+#define lockdep_assert_not_held(l)		do { (void)(l); } while (0)
 #define lockdep_assert_held(l)			do { (void)(l); } while (0)
-#define lockdep_assert_held_write(l)	do { (void)(l); } while (0)
+#define lockdep_assert_held_write(l)		do { (void)(l); } while (0)
 #define lockdep_assert_held_read(l)		do { (void)(l); } while (0)
 #define lockdep_assert_held_once(l)		do { (void)(l); } while (0)
 

-- 
2.27.0

ath10k_drain_tx() must not be called with conf_mutex held as workers can
use that also. Add call to lockdep_assert_not_held() on conf_mutex to
detect if conf_mutex is held by the caller.

The idea for this patch stemmed from coming across the comment block
above the ath10k_drain_tx() while reviewing the conf_mutex holds during
to debug the conf_mutex lock assert in ath10k_debug_fw_stats_request().

Adding detection to assert on conf_mutex hold will help detect incorrect
usages that could lead to locking problems when async worker routines try
to call this routine.

Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
---
 drivers/net/wireless/ath/ath10k/mac.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
index c202b167d8c6..7de05b679ad2 100644
--- a/drivers/net/wireless/ath/ath10k/mac.c
+++ b/drivers/net/wireless/ath/ath10k/mac.c

@@ -4728,6 +4728,8 @@ static void ath10k_mac_op_wake_tx_queue(struct ieee80211_hw *hw,
 /* Must not be called with conf_mutex held as workers can use that also. */
 void ath10k_drain_tx(struct ath10k *ar)
 {
+	lockdep_assert_not_held(&ar->conf_mutex);
+
 	/* make sure rcu-protected mac80211 tx path itself is drained */
 	synchronize_net();
 

-- 
2.27.0

On Fri, Feb 12, 2021 at 04:28:42PM -0700, Shuah Khan wrote:

+#define lockdep_assert_not_held(l)	do {			\
+		WARN_ON(debug_locks && lockdep_is_held(l));	\
+	} while (0)
+

This thing isn't as straight forward as you might think, but it'll
mostly work.

Notably this thing will misfire when lockdep_off() is employed. It
certainyl needs a comment to explain the subtleties.

On Sun, Feb 14, 2021 at 06:53:01PM +0100, Peter Zijlstra wrote:

On Fri, Feb 12, 2021 at 04:28:42PM -0700, Shuah Khan wrote:

quoted

+#define lockdep_assert_not_held(l)	do {			\
+		WARN_ON(debug_locks && lockdep_is_held(l));	\
+	} while (0)
+

This thing isn't as straight forward as you might think, but it'll
mostly work.

Notably this thing will misfire when lockdep_off() is employed. It
certainyl needs a comment to explain the subtleties.

I think something like so will work, but please double check.

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..c8b0d292bf8e 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h

@@ -294,11 +294,15 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
 
 #define lockdep_depth(tsk)	(debug_locks ? (tsk)->lockdep_depth : 0)
 
-#define lockdep_assert_held(l)	do {				\
-		WARN_ON(debug_locks && !lockdep_is_held(l));	\
+#define lockdep_assert_held(l)	do {					\
+		WARN_ON(debug_locks && lockdep_is_held(l) == 0));	\
 	} while (0)
 
-#define lockdep_assert_held_write(l)	do {			\
+#define lockdep_assert_not_held(l)	do {				\
+		WARN_ON(debug_locks && lockdep_is_held(l) == 1));	\
+	} while (0)
+
+#define lockdep_assert_held_write(l)	do {				\
 		WARN_ON(debug_locks && !lockdep_is_held_type(l, 0));	\
 	} while (0)
 

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c1418b47f625..983ba206f7b2 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c

@@ -5467,7 +5467,7 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
 	int ret = 0;
 
 	if (unlikely(!lockdep_enabled()))
-		return 1; /* avoid false negative lockdep_assert_held() */
+		return -1; /* avoid false negative lockdep_assert_held() */
 
 	raw_local_irq_save(flags);
 	check_flags(flags);