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().

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

Changes since v2:
-- Fixed coding style issues
-- Patch 2 uses new lock states in __lock_is_held() and
lock_is_held_type

Patch 1 incorporates suggestions from Peter Zijlstra on v1 series to avoid misfires when lockdep_off() is employed.

Patch 2 Johannes Berg's suggestions as it make it easier to read and maintain the lock states. These are defines and a enum to avoid changes to lock_is_held_type() and lockdep_is_held() return types.

Patch 2 is a separate patch because it adds defines to lockdep.h and kernel/locking/lockdep.c now includes lockdep.h - decided make this a separate patch just in case issues related to header dependencies pop up. I can combine Patches 1&2 if that is preferred.

Patch 3 uses the new interface in ath10k_drain_tx() function. Added Kalle Valo's Ack from v1 for this change.

Tested on the mainline from yesterday.

Shuah Khan (3):
lockdep: add lockdep_assert_not_held()
lockdep: add lockdep lock state defines
ath10k: detect conf_mutex held ath10k_drain_tx() calls

 drivers/net/wireless/ath/ath10k/mac.c |  2 ++
 include/linux/lockdep.h               | 18 +++++++++++++++---
 kernel/locking/lockdep.c              | 15 ++++++++++-----
 3 files changed, 27 insertions(+), 8 deletions(-)

2.27.0


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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.

---
 drivers/net/wireless/ath/ath10k/mac.c | 2 ++
 1 file changed, 2 insertions(+)

index bb6c5ee43ac0..5ce4f8d038b9 100644
@@ -4727,6 +4727,8 @@ 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


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Some kernel functions must be called without holding a specific lock. 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.

Incorporates suggestions from Peter Zijlstra to avoid misfires when lockdep_off() is employed.

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().

---
 include/linux/lockdep.h  | 11 ++++++++---
 kernel/locking/lockdep.c |  6 +++++-
 2 files changed, 13 insertions(+), 4 deletions(-)

index 7b7ebf2e28ec..dbd9ea846b36 100644
@@ -301,8 +301,12 @@ 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_not_held(l)	do {				\
+		WARN_ON(debug_locks && lockdep_is_held(l) == 1);	\
 	} while (0)
 
 #define lockdep_assert_held_write(l)	do {			\

@@ -393,7 +397,8 @@ extern int lockdep_is_held(const void *);
 #define lockdep_is_held_type(l, r)		(1)
 
 #define lockdep_assert_held(l)			do { (void)(l); } while (0)
-#define lockdep_assert_held_write(l)	do { (void)(l); } while (0)
+#define lockdep_assert_not_held(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)
 

index c6d0c1dc6253..818d0ceed3eb 100644
@@ -5539,8 +5539,12 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
 	unsigned long flags;
 	int ret = 0;
 
+	/*
+	 * avoid false negative lockdep_assert_held() and
+	 * lockdep_assert_not_held()
+	 */
 	if (unlikely(!lockdep_enabled()))
-		return 1; /* avoid false negative lockdep_assert_held() */
+		return -1;
 
 	raw_local_irq_save(flags);
 	check_flags(flags);

2.27.0


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Adds defines for lock state returns from lock_is_held_type() based on Johannes Berg's suggestions as it make it easier to read and maintain the lock states. These are defines and a enum to avoid changes to lock_is_held_type() and lockdep_is_held() return types.

Updates to lock_is_held_type() and __lock_is_held() to use the new defines.

---
 include/linux/lockdep.h  | 11 +++++++++--
 kernel/locking/lockdep.c | 11 ++++++-----
 2 files changed, 15 insertions(+), 7 deletions(-)

index dbd9ea846b36..17805aac0e85 100644
@@ -268,6 +268,11 @@ extern void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 
 extern void lock_release(struct lockdep_map *lock, unsigned long ip);
 
+/* lock_is_held_type() returns */
+#define LOCK_STATE_UNKNOWN	-1
+#define LOCK_STATE_NOT_HELD	0
+#define LOCK_STATE_HELD		1
+
 /*
  * Same "read" as for lock_acquire(), except -1 means any.
  */

@@ -302,11 +307,13 @@ 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) == 0);	\
+		WARN_ON(debug_locks &&					\
+			lockdep_is_held(l) == LOCK_STATE_NOT_HELD);	\
 	} while (0)
 
 #define lockdep_assert_not_held(l)	do {				\
-		WARN_ON(debug_locks && lockdep_is_held(l) == 1);	\
+		WARN_ON(debug_locks &&					\
+			lockdep_is_held(l) == LOCK_STATE_HELD);		\
 	} while (0)
 
 #define lockdep_assert_held_write(l)	do {			\

index 818d0ceed3eb..f5a8200f24f1 100644
@@ -54,6 +54,7 @@
 #include <linux/nmi.h>
 #include <linux/rcupdate.h>
 #include <linux/kprobes.h>
+#include <linux/lockdep.h>
 
 #include <asm/sections.h>
 

@@ -5252,13 +5253,13 @@ int __lock_is_held(const struct lockdep_map *lock, int read)
 
 		if (match_held_lock(hlock, lock)) {
 			if (read == -1 || hlock->read == read)
-				return 1;
+				return LOCK_STATE_HELD;
 
-			return 0;
+			return LOCK_STATE_NOT_HELD;
 		}
 	}
 
-	return 0;
+	return LOCK_STATE_NOT_HELD;
 }
 
 static struct pin_cookie __lock_pin_lock(struct lockdep_map *lock)

@@ -5537,14 +5538,14 @@ EXPORT_SYMBOL_GPL(lock_release);
 noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
 {
 	unsigned long flags;
-	int ret = 0;
+	int ret = LOCK_STATE_NOT_HELD;
 
 	/*
 	 * avoid false negative lockdep_assert_held() and
 	 * lockdep_assert_not_held()
 	 */
 	if (unlikely(!lockdep_enabled()))
-		return -1;
+		return LOCK_STATE_UNKNOWN;
 
 	raw_local_irq_save(flags);
 	check_flags(flags);

2.27.0


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Thanks!

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Via which tree should these go?

https://patchwork.kernel.org/project/linux-wireless/list/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches

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I've just queued the lot for locking/core, which will show up in tip when the robots don't hate on it.

Does that work for you?

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That's perfect, thanks! Just making sure that the patches don't get lost.

https://patchwork.kernel.org/project/linux-wireless/list/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches

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Awesome. Thank you.

thanks,
-- Shuah

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