[PATCH v2 0/3] Add lockdep_assert_not_held()

[PATCH v2 0/3] Add lockdep_assert_not_held()

[Shuah Khan]

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/lkml/37a29c383bff2fb1605241ee6c7c9be3784fb3c6.1613171185.git.skhan@linuxfoundation.org/
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.

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              |  6 +++++-
 3 files changed, 22 insertions(+), 4 deletions(-)

-- 
2.27.0


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[PATCH v2 1/3] lockdep: add lockdep_assert_not_held()

[Shuah Khan]

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().

Link: https://lore.kernel.org/lkml/37a29c383bff2fb1605241ee6c7c9be3784fb3c6.1613171185.git.skhan@linuxfoundation.org/
Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
---
 include/linux/lockdep.h  | 11 ++++++++---
 kernel/locking/lockdep.c |  5 ++++-
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..93eb5f797fc1 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -294,8 +294,12 @@ 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 {			\
@@ -384,7 +388,8 @@ 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)
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index bdaf4829098c..d3299fd85c4a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5472,7 +5472,10 @@ 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() */
+		/* avoid false negative lockdep_assert_not_held()
+		 * and lockdep_assert_held()
+		 */
+		return -1;
 
 	raw_local_irq_save(flags);
 	check_flags(flags);
-- 
2.27.0


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Re: [PATCH v2 1/3] lockdep: add lockdep_assert_not_held()

[Peter Zijlstra]

On Fri, Feb 26, 2021 at 10:52:13AM -0700, Shuah Khan wrote:
> +		/* avoid false negative lockdep_assert_not_held()
> +		 * and lockdep_assert_held()
> +		 */

That's a coding style fail.

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Re: [PATCH v2 1/3] lockdep: add lockdep_assert_not_held()

[Shuah Khan]

On 2/26/21 2:07 PM, Peter Zijlstra wrote:
> On Fri, Feb 26, 2021 at 10:52:13AM -0700, Shuah Khan wrote:
>> +		/* avoid false negative lockdep_assert_not_held()
>> +		 * and lockdep_assert_held()
>> +		 */
> 
> That's a coding style fail.
> 

Checkpatch didn't complain. What's your preference? Does the
following work for you?

/*
  * avoid false negative lockdep_assert_not_held()
  * and lockdep_assert_held()
  */

thanks,
-- Shuah

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Re: [PATCH v2 1/3] lockdep: add lockdep_assert_not_held()

[Peter Zijlstra]

On Fri, Feb 26, 2021 at 02:16:12PM -0700, Shuah Khan wrote:
> On 2/26/21 2:07 PM, Peter Zijlstra wrote:
> > On Fri, Feb 26, 2021 at 10:52:13AM -0700, Shuah Khan wrote:
> > > +		/* avoid false negative lockdep_assert_not_held()
> > > +		 * and lockdep_assert_held()
> > > +		 */
> > 
> > That's a coding style fail.
> > 
> 
> Checkpatch didn't complain.

  Documentation/CodingStyle

(or whatever unreadable rst crap it is today :-( )

and:

  https://lkml.kernel.org/lkml/CA+55aFyQYJerovMsSoSKS7PessZBr4vNp-3QUUwhqk4A4_jcbg@mail.gmail.com/

> What's your preference? Does the following work for you?
> 
> /*
>  * avoid false negative lockdep_assert_not_held()
>  * and lockdep_assert_held()
>  */

Yep (ideally even with a Capital and full stop).

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[PATCH v2 2/3] lockdep: add lockdep lock state defines

[Shuah Khan]

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.

Link: https://lore.kernel.org/lkml/37a29c383bff2fb1605241ee6c7c9be3784fb3c6.1613171185.git.skhan@linuxfoundation.org/
Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
---
 include/linux/lockdep.h  | 11 +++++++++--
 kernel/locking/lockdep.c |  3 ++-
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 93eb5f797fc1..7c2622854152 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -261,6 +261,11 @@ 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.
  */
@@ -295,11 +300,13 @@ 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 {			\
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index d3299fd85c4a..e3898c888ad2 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -54,6 +54,7 @@
 #include <linux/nmi.h>
 #include <linux/rcupdate.h>
 #include <linux/kprobes.h>
+#include <linux/lockdep.h>
 
 #include <asm/sections.h>
 
@@ -5475,7 +5476,7 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
 		/* avoid false negative lockdep_assert_not_held()
 		 * and lockdep_assert_held()
 		 */
-		return -1;
+		return LOCK_STATE_UNKNOWN;
 
 	raw_local_irq_save(flags);
 	check_flags(flags);
-- 
2.27.0


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Re: [PATCH v2 2/3] lockdep: add lockdep lock state defines

[Johannes Berg]

> @@ -5475,7 +5476,7 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
>  		/* avoid false negative lockdep_assert_not_held()
>  		 * and lockdep_assert_held()
>  		 */
> -		return -1;
> +		return LOCK_STATE_UNKNOWN;

I'd argue that then the other two return places here should also be
changed.

johannes


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Re: [PATCH v2 2/3] lockdep: add lockdep lock state defines

[Shuah Khan]

On 2/26/21 11:03 AM, Johannes Berg wrote:
> 
>> @@ -5475,7 +5476,7 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
>>   		/* avoid false negative lockdep_assert_not_held()
>>   		 * and lockdep_assert_held()
>>   		 */
>> -		return -1;
>> +		return LOCK_STATE_UNKNOWN;
> 
> I'd argue that then the other two return places here should also be
> changed.
> 

Makes sense.

Since lock_is_held_type() simply returns what  __lock_is_held() for the
other cases, __lock_is_held() is the one that needs changes to use these 
defines.

thanks,
-- Shuah





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[PATCH v2 3/3] ath10k: detect conf_mutex held ath10k_drain_tx() calls

[Shuah Khan]

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/lkml/37a29c383bff2fb1605241ee6c7c9be3784fb3c6.1613171185.git.skhan@linuxfoundation.org/
Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/
Acked-by: Kalle Valo <kvalo@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 7d98250380ec..a595ff4f0843 100644
--- a/drivers/net/wireless/ath/ath10k/mac.c
+++ b/drivers/net/wireless/ath/ath10k/mac.c
@@ -4567,6 +4567,8 @@ 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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