Q: lockdep_assert_held_read() after downgrade_write()

Q: lockdep_assert_held_read() after downgrade_write()

[J. R. Okajima]

Peter Zijlstra,

May I ask you a question?
v4.10-rc1 got a commit
	f831948 2016-11-30 locking/lockdep: Provide a type check for lock_is_held
I've tested a little and lockdep splat a stack trace.

{
	DECLARE_RWSEM(rw);
	static struct lock_class_key key;
	lockdep_set_class(&rw, &key);

	down_read(&rw);
	lockdep_assert_held_read(&rw);
	up_read(&rw);

	down_write(&rw);
	lockdep_assert_held_exclusive(&rw);
	up_write(&rw);

	downgrade_write(&rw);
	lockdep_assert_held_read(&rw);	<-- here
	up_read(&rw);
}

I was expecting that lockdep_assert_held_read() splat nothing after
downgrade_write(). Is this warning an intentional behaviour?

Also the final up_read() gives me a warning too. It is produced at
	lockdep.c:3514:lock_release(): DEBUG_LOCKS_WARN_ON(depth <= 0)

As an additional information, I increased some lockdep constants.
Do you think this is related?

include/linux/lockdep.h
+#define MAX_LOCKDEP_SUBCLASSES		(8UL + 4)
+#define MAX_LOCKDEP_KEYS_BITS		(13 + 3)

kernel/locking/lockdep_internals.h
+#define MAX_LOCKDEP_ENTRIES	(32768UL << 5)
+#define MAX_LOCKDEP_CHAINS_BITS	(16 + 5)
+#define MAX_STACK_TRACE_ENTRIES	(524288UL << 5)


J. R. Okajima

Re: Q: lockdep_assert_held_read() after downgrade_write()

[Jens Axboe]

On 01/30/2017 02:25 PM, J. R. Okajima wrote:
> Peter Zijlstra,
> 
> May I ask you a question?
> v4.10-rc1 got a commit
> 	f831948 2016-11-30 locking/lockdep: Provide a type check for lock_is_held
> I've tested a little and lockdep splat a stack trace.
> 
> {
> 	DECLARE_RWSEM(rw);
> 	static struct lock_class_key key;
> 	lockdep_set_class(&rw, &key);
> 
> 	down_read(&rw);
> 	lockdep_assert_held_read(&rw);
> 	up_read(&rw);
> 
> 	down_write(&rw);
> 	lockdep_assert_held_exclusive(&rw);
> 	up_write(&rw);
> 
> 	downgrade_write(&rw);
> 	lockdep_assert_held_read(&rw);	<-- here
> 	up_read(&rw);
> }
> 
> I was expecting that lockdep_assert_held_read() splat nothing after
> downgrade_write(). Is this warning an intentional behaviour?
> 
> Also the final up_read() gives me a warning too. It is produced at
> 	lockdep.c:3514:lock_release(): DEBUG_LOCKS_WARN_ON(depth <= 0)

I don't think you understand how it works. downgrade_write() turns a write
lock into read held. To make that last sequence valid, you'd need:

	down_write(&rw);
	downgrade_write(&rw);
	lockdep_assert_held_read(&rw)
	up_read(&rw);

or just not drop up_write() from the last section.

-- 
Jens Axboe

Re: Q: lockdep_assert_held_read() after downgrade_write()

[Peter Zijlstra]

On Mon, Jan 30, 2017 at 02:30:45PM -0700, Jens Axboe wrote:
> On 01/30/2017 02:25 PM, J. R. Okajima wrote:
> > Peter Zijlstra,
> > 
> > May I ask you a question?
> > v4.10-rc1 got a commit
> > 	f831948 2016-11-30 locking/lockdep: Provide a type check for lock_is_held
> > I've tested a little and lockdep splat a stack trace.
> > 
> > {
> > 	DECLARE_RWSEM(rw);
> > 	static struct lock_class_key key;
> > 	lockdep_set_class(&rw, &key);
> > 
> > 	down_read(&rw);
> > 	lockdep_assert_held_read(&rw);
> > 	up_read(&rw);
> > 
> > 	down_write(&rw);
> > 	lockdep_assert_held_exclusive(&rw);
> > 	up_write(&rw);
> > 
> > 	downgrade_write(&rw);
> > 	lockdep_assert_held_read(&rw);	<-- here
> > 	up_read(&rw);
> > }
> > 
> > I was expecting that lockdep_assert_held_read() splat nothing after
> > downgrade_write(). Is this warning an intentional behaviour?
> > 
> > Also the final up_read() gives me a warning too. It is produced at
> > 	lockdep.c:3514:lock_release(): DEBUG_LOCKS_WARN_ON(depth <= 0)
> 
> I don't think you understand how it works. downgrade_write() turns a write
> lock into read held. To make that last sequence valid, you'd need:

Correct, and I'm surprised that didn't explode in different ways.

> 
> 	down_write(&rw);
> 	downgrade_write(&rw);
> 	lockdep_assert_held_read(&rw)
> 	up_read(&rw);
> 
> or just not drop up_write() from the last section.

Right, but also, there seems to be a missing lockdep annotation to make
that work. That is, downgrade_write() doesn't have a lockdep annotation,
so it (lockdep) will still think its a write lock.


Let me try and fix both issues.

Re: Q: lockdep_assert_held_read() after downgrade_write()

[Peter Zijlstra]

On Tue, Jan 31, 2017 at 11:36:20AM +0100, Peter Zijlstra wrote:
> On Mon, Jan 30, 2017 at 02:30:45PM -0700, Jens Axboe wrote:

> > I don't think you understand how it works. downgrade_write() turns a write
> > lock into read held. To make that last sequence valid, you'd need:
> 
> Correct, and I'm surprised that didn't explode in different ways.
> 
> > 
> > 	down_write(&rw);
> > 	downgrade_write(&rw);
> > 	lockdep_assert_held_read(&rw)
> > 	up_read(&rw);
> > 
> > or just not drop up_write() from the last section.
> 
> Right, but also, there seems to be a missing lockdep annotation to make
> that work. That is, downgrade_write() doesn't have a lockdep annotation,
> so it (lockdep) will still think its a write lock.
> 
> 
> Let me try and fix both issues.

Something like so I suppose,... completely untested.

There could be a good reason for the current lockdep behaviour, but I
cannot remember.

---
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 45ba475d4be3..dfa9e40f83d5 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -123,10 +123,9 @@ EXPORT_SYMBOL(up_write);
  */
 void downgrade_write(struct rw_semaphore *sem)
 {
-	/*
-	 * lockdep: a downgraded write will live on as a write
-	 * dependency.
-	 */
+	rwsem_release(&sem->dep_map, 1, _RET_IP_);
+	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
+
 	rwsem_set_reader_owned(sem);
 	__downgrade_write(sem);
 }
diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
index a699f4048ba1..3bd584c81b0b 100644
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -40,8 +40,10 @@ static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
 	 * do a write to the rwsem cacheline when it is really necessary
 	 * to minimize cacheline contention.
 	 */
-	if (sem->owner != RWSEM_READER_OWNED)
+	if (sem->owner != RWSEM_READER_OWNED) {
+		WARN_ON_ONCE(sem->owner != current);
 		WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);
+	}
 }
 
 static inline bool rwsem_owner_is_writer(struct task_struct *owner)

Re: Q: lockdep_assert_held_read() after downgrade_write()

[Waiman Long]

On 01/31/2017 06:25 AM, Peter Zijlstra wrote:
> On Tue, Jan 31, 2017 at 11:36:20AM +0100, Peter Zijlstra wrote:
>> On Mon, Jan 30, 2017 at 02:30:45PM -0700, Jens Axboe wrote:
>>> I don't think you understand how it works. downgrade_write() turns a write
>>> lock into read held. To make that last sequence valid, you'd need:
>> Correct, and I'm surprised that didn't explode in different ways.
>>
>>> 	down_write(&rw);
>>> 	downgrade_write(&rw);
>>> 	lockdep_assert_held_read(&rw)
>>> 	up_read(&rw);
>>>
>>> or just not drop up_write() from the last section.
>> Right, but also, there seems to be a missing lockdep annotation to make
>> that work. That is, downgrade_write() doesn't have a lockdep annotation,
>> so it (lockdep) will still think its a write lock.
>>
>>
>> Let me try and fix both issues.
> Something like so I suppose,... completely untested.
>
> There could be a good reason for the current lockdep behaviour, but I
> cannot remember.
>
> ---
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index 45ba475d4be3..dfa9e40f83d5 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -123,10 +123,9 @@ EXPORT_SYMBOL(up_write);
>   */
>  void downgrade_write(struct rw_semaphore *sem)
>  {
> -	/*
> -	 * lockdep: a downgraded write will live on as a write
> -	 * dependency.
> -	 */
> +	rwsem_release(&sem->dep_map, 1, _RET_IP_);
> +	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
> +
>  	rwsem_set_reader_owned(sem);
>  	__downgrade_write(sem);
>  }
> diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
> index a699f4048ba1..3bd584c81b0b 100644
> --- a/kernel/locking/rwsem.h
> +++ b/kernel/locking/rwsem.h
> @@ -40,8 +40,10 @@ static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
>  	 * do a write to the rwsem cacheline when it is really necessary
>  	 * to minimize cacheline contention.
>  	 */
> -	if (sem->owner != RWSEM_READER_OWNED)
> +	if (sem->owner != RWSEM_READER_OWNED) {
> +		WARN_ON_ONCE(sem->owner != current);
>  		WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);
> +	}
>  }
>  
>  static inline bool rwsem_owner_is_writer(struct task_struct *owner)

I don't think you can do a WARN_ON_ONCE() check for sem->owner !=
current here. If the rwsem starts from an unlock state, sem->owner will
be NULL and an incorrect warning message will be printed.

Cheers,
Longman

Re: Q: lockdep_assert_held_read() after downgrade_write()

[Peter Zijlstra]

On Tue, Jan 31, 2017 at 09:23:08AM -0500, Waiman Long wrote:
> On 01/31/2017 06:25 AM, Peter Zijlstra wrote:
> > @@ -40,8 +40,10 @@ static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
> >  	 * do a write to the rwsem cacheline when it is really necessary
> >  	 * to minimize cacheline contention.
> >  	 */
> > -	if (sem->owner != RWSEM_READER_OWNED)
> > +	if (sem->owner != RWSEM_READER_OWNED) {
> > +		WARN_ON_ONCE(sem->owner != current);
> >  		WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);
> > +	}
> >  }
> >  
> >  static inline bool rwsem_owner_is_writer(struct task_struct *owner)
> 
> I don't think you can do a WARN_ON_ONCE() check for sem->owner !=
> current here. If the rwsem starts from an unlock state, sem->owner will
> be NULL and an incorrect warning message will be printed.

Argh, I only looked at the downgrade_write() user and forgot to look if
it was used elsewhere.

Re: Q: lockdep_assert_held_read() after downgrade_write()

[J. R. Okajima]

Jens Axboe:
> I don't think you understand how it works. downgrade_write() turns a write
> lock into read held. To make that last sequence valid, you'd need:
>
> 	down_write(&rw);
> 	downgrade_write(&rw);
> 	lockdep_assert_held_read(&rw)
> 	up_read(&rw);
>
> or just not drop up_write() from the last section.

Arg...
It is my bonehead mistake that I inserted up_write() before
downgrade_write(). Sorry about that.
Fortunately Peter Zijlstra reviewed downgrade_write() and sent a
patch. Thank you, it passed my first test.

Now allow me going on the second test (based upon Peter's patch)

- two rwsem, rwA and rwB.
- the locking order is rwA first, and then rwB.
- good case
  down_read(rwA)
  down_read(rwB)
  up_read(rwB)
  up_read(rwA)

  down_write(rwA)
  down_write(rwB)
  up_write(rwB)
  up_write(rwA)

- questionable case
  down_write(rwA)
  down_write(rwB)
  downgrade_write(rwA)
  downgrade_write(rwB)
  up_read(rwB)
  up_read(rwA)

These two downgrade_write() have their strict order? If so, what is
that?
Do the added two lines
+	rwsem_release(&sem->dep_map, 1, _RET_IP_);
+	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
produce a traditional AB-BA deadlock warning, don't they?


J. R. Okajima

Re: Q: lockdep_assert_held_read() after downgrade_write()

[Peter Zijlstra]

On Wed, Feb 01, 2017 at 12:40:03AM +0900, J. R. Okajima wrote:

> Now allow me going on the second test (based upon Peter's patch)
> 
> - two rwsem, rwA and rwB.
> - the locking order is rwA first, and then rwB.
> - good case
>   down_read(rwA)
>   down_read(rwB)
>   up_read(rwB)
>   up_read(rwA)
> 
>   down_write(rwA)
>   down_write(rwB)
>   up_write(rwB)
>   up_write(rwA)
> 
> - questionable case
>   down_write(rwA)
>   down_write(rwB)
>   downgrade_write(rwA)
>   downgrade_write(rwB)
>   up_read(rwB)
>   up_read(rwA)
> 
> These two downgrade_write() have their strict order? If so, what is
> that?
> Do the added two lines
> +	rwsem_release(&sem->dep_map, 1, _RET_IP_);
> +	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
> produce a traditional AB-BA deadlock warning, don't they?

Blergh, yes, because we do a full release.

Does something like the below work better? The annotation in
downgrade_write() would look something like:

+	lock_downgrade(&sem->dep_map, 1, _RET_IP_);

Not even compile tested and lacks the !LOCKDEP build bits.

---
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 1e327bb..76cf149 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -361,6 +361,8 @@ static inline void lock_set_subclass(struct lockdep_map *lock,
 	lock_set_class(lock, lock->name, lock->key, subclass, ip);
 }
 
+extern void lock_downgrade(struct lockdep_map *lock, int read, unsigned long ip);
+
 extern void lockdep_set_current_reclaim_state(gfp_t gfp_mask);
 extern void lockdep_clear_current_reclaim_state(void);
 extern void lockdep_trace_alloc(gfp_t mask);
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7c38f8f..88517b6 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3488,6 +3488,63 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 	return 1;
 }
 
+static int __lock_downgrade(struct lockdep_map *lock, int read, unsigned long ip)
+{
+	struct task_struct *curr = current;
+	struct held_lock *hlock, *prev_hlock;
+	struct lock_class *class;
+	unsigned int depth;
+	int i;
+
+	depth = curr->lockdep_depth;
+	/*
+	 * This function is about (re)setting the class of a held lock,
+	 * yet we're not actually holding any locks. Naughty user!
+	 */
+	if (DEBUG_LOCKS_WARN_ON(!depth))
+		return 0;
+
+	prev_hlock = NULL;
+	for (i = depth-1; i >= 0; i--) {
+		hlock = curr->held_locks + i;
+		/*
+		 * We must not cross into another context:
+		 */
+		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
+			break;
+		if (match_held_lock(hlock, lock))
+			goto found_it;
+		prev_hlock = hlock;
+	}
+	return print_unlock_imbalance_bug(curr, lock, ip);
+
+found_it:
+	curr->lockdep_depth = i;
+	curr->curr_chain_key = hlock->prev_chain_key;
+
+	WARN(hlock->read, "downgrading a read lock");
+	hlock->read = read;
+	hlock->acquire_ip = ip;
+
+	for (; i < depth; i++) {
+		hlock = curr->held_locks + i;
+		if (!__lock_acquire(hlock->instance,
+			hlock_class(hlock)->subclass, hlock->trylock,
+				hlock->read, hlock->check, hlock->hardirqs_off,
+				hlock->nest_lock, hlock->acquire_ip,
+				hlock->references, hlock->pin_count))
+			return 0;
+	}
+
+	/*
+	 * I took it apart and put it back together again, except now I have
+	 * these 'spare' parts.. where shall I put them.
+	 */
+	if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
+		return 0;
+	return 1;
+}
+
 /*
  * Remove the lock to the list of currently held locks - this gets
  * called on mutex_unlock()/spin_unlock*() (or on a failed
@@ -3732,6 +3789,23 @@ void lock_set_class(struct lockdep_map *lock, const char *name,
 }
 EXPORT_SYMBOL_GPL(lock_set_class);
 
+void lock_downgrade(struct lockdep_map *lock, int read, unsigned long ip)
+{
+	unsigned long flags;
+
+	if (unlikely(current->lockdep_recursion))
+		return;
+
+	raw_local_irq_save(flags);
+	current->lockdep_recursion = 1;
+	check_flags(flags);
+	if (__lock_downgrade(lock, read, ip))
+		check_chain_key(current);
+	current->lockdep_recursion = 0;
+	raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lock_downgrade);
+
 /*
  * We are not always called with irqs disabled - do that here,
  * and also avoid lockdep recursion:

Re: Q: lockdep_assert_held_read() after downgrade_write()

[J. R. Okajima]

Peter Zijlstra:
> Does something like the below work better? The annotation in
> downgrade_write() would look something like:
>
> +	lock_downgrade(&sem->dep_map, 1, _RET_IP_);
>
> Not even compile tested and lacks the !LOCKDEP build bits.

Thanks for the patch.
It seems working expectedly. I began writing a similar patch locally
with minor consolidations by adding a new function or two. I will send a
patch series. Please review and merge them into v4.10. If you don't like
the patch, especially the new function name, feel free to change it.
I don't know whether !LOCKDEP build bits are necessary or not.


J. R. Okajima

[PATCH 1/3] lockdep: consolidate by new find_held_lock()

[J. R. Okajima]

A simple consolidataion. The behaviour should not change.

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
---
 kernel/locking/lockdep.c | 114 ++++++++++++++++++++++-------------------------
 1 file changed, 54 insertions(+), 60 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 85d9222..b7a2001 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3428,13 +3428,49 @@ static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
 	return 0;
 }
 
+/* @depth must not be zero */
+static struct held_lock *find_held_lock(struct task_struct *curr,
+					struct lockdep_map *lock,
+					unsigned int depth, int *idx)
+{
+	struct held_lock *ret, *hlock, *prev_hlock;
+	int i;
+
+	i = depth - 1;
+	hlock = curr->held_locks + i;
+	ret = hlock;
+	if (match_held_lock(hlock, lock))
+		goto out;
+
+	ret = NULL;
+	for (i--, prev_hlock = hlock--;
+	     i >= 0;
+	     i--, prev_hlock = hlock--) {
+		/*
+		 * We must not cross into another context:
+		 */
+		if (prev_hlock->irq_context != hlock->irq_context) {
+			ret = NULL;
+			break;
+		}
+		if (match_held_lock(hlock, lock)) {
+			ret = hlock;
+			break;
+		}
+	}
+
+out:
+	*idx = i;
+	return ret;
+}
+
 static int
 __lock_set_class(struct lockdep_map *lock, const char *name,
 		 struct lock_class_key *key, unsigned int subclass,
 		 unsigned long ip)
 {
 	struct task_struct *curr = current;
-	struct held_lock *hlock, *prev_hlock;
+	struct held_lock *hlock;
 	struct lock_class *class;
 	unsigned int depth;
 	int i;
@@ -3447,21 +3483,10 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 	if (DEBUG_LOCKS_WARN_ON(!depth))
 		return 0;
 
-	prev_hlock = NULL;
-	for (i = depth-1; i >= 0; i--) {
-		hlock = curr->held_locks + i;
-		/*
-		 * We must not cross into another context:
-		 */
-		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
-			break;
-		if (match_held_lock(hlock, lock))
-			goto found_it;
-		prev_hlock = hlock;
-	}
-	return print_unlock_imbalance_bug(curr, lock, ip);
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock)
+		return print_unlock_imbalance_bug(curr, lock, ip);
 
-found_it:
 	lockdep_init_map(lock, name, key, 0);
 	class = register_lock_class(lock, subclass, 0);
 	hlock->class_idx = class - lock_classes + 1;
@@ -3499,7 +3524,7 @@ static int
 __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
 {
 	struct task_struct *curr = current;
-	struct held_lock *hlock, *prev_hlock;
+	struct held_lock *hlock;
 	unsigned int depth;
 	int i;
 
@@ -3518,21 +3543,10 @@ __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
 	 * Check whether the lock exists in the current stack
 	 * of held locks:
 	 */
-	prev_hlock = NULL;
-	for (i = depth-1; i >= 0; i--) {
-		hlock = curr->held_locks + i;
-		/*
-		 * We must not cross into another context:
-		 */
-		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
-			break;
-		if (match_held_lock(hlock, lock))
-			goto found_it;
-		prev_hlock = hlock;
-	}
-	return print_unlock_imbalance_bug(curr, lock, ip);
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock)
+		return print_unlock_imbalance_bug(curr, lock, ip);
 
-found_it:
 	if (hlock->instance == lock)
 		lock_release_holdtime(hlock);
 
@@ -3894,7 +3908,7 @@ static void
 __lock_contended(struct lockdep_map *lock, unsigned long ip)
 {
 	struct task_struct *curr = current;
-	struct held_lock *hlock, *prev_hlock;
+	struct held_lock *hlock;
 	struct lock_class_stats *stats;
 	unsigned int depth;
 	int i, contention_point, contending_point;
@@ -3907,22 +3921,12 @@ __lock_contended(struct lockdep_map *lock, unsigned long ip)
 	if (DEBUG_LOCKS_WARN_ON(!depth))
 		return;
 
-	prev_hlock = NULL;
-	for (i = depth-1; i >= 0; i--) {
-		hlock = curr->held_locks + i;
-		/*
-		 * We must not cross into another context:
-		 */
-		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
-			break;
-		if (match_held_lock(hlock, lock))
-			goto found_it;
-		prev_hlock = hlock;
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock) {
+		print_lock_contention_bug(curr, lock, ip);
+		return;
 	}
-	print_lock_contention_bug(curr, lock, ip);
-	return;
 
-found_it:
 	if (hlock->instance != lock)
 		return;
 
@@ -3946,7 +3950,7 @@ static void
 __lock_acquired(struct lockdep_map *lock, unsigned long ip)
 {
 	struct task_struct *curr = current;
-	struct held_lock *hlock, *prev_hlock;
+	struct held_lock *hlock;
 	struct lock_class_stats *stats;
 	unsigned int depth;
 	u64 now, waittime = 0;
@@ -3960,22 +3964,12 @@ __lock_acquired(struct lockdep_map *lock, unsigned long ip)
 	if (DEBUG_LOCKS_WARN_ON(!depth))
 		return;
 
-	prev_hlock = NULL;
-	for (i = depth-1; i >= 0; i--) {
-		hlock = curr->held_locks + i;
-		/*
-		 * We must not cross into another context:
-		 */
-		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
-			break;
-		if (match_held_lock(hlock, lock))
-			goto found_it;
-		prev_hlock = hlock;
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock) {
+		print_lock_contention_bug(curr, lock, _RET_IP_);
+		return;
 	}
-	print_lock_contention_bug(curr, lock, _RET_IP_);
-	return;
 
-found_it:
 	if (hlock->instance != lock)
 		return;
 
-- 
2.1.4

[PATCH 2/3] lockdep: consolidate by new validate_held_lock()

[J. R. Okajima]

A simple consolidataion. The behaviour should not change.

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
---
 kernel/locking/lockdep.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index b7a2001..7dc8f8e 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3464,6 +3464,23 @@ static struct held_lock *find_held_lock(struct task_struct *curr,
 	return ret;
 }
 
+static int validate_held_lock(struct task_struct *curr, unsigned int depth,
+			      int idx)
+{
+	struct held_lock *hlock;
+
+	for (hlock = curr->held_locks + idx; idx < depth; idx++, hlock++)
+		if (!__lock_acquire(hlock->instance,
+				    hlock_class(hlock)->subclass,
+				    hlock->trylock,
+				    hlock->read, hlock->check,
+				    hlock->hardirqs_off,
+				    hlock->nest_lock, hlock->acquire_ip,
+				    hlock->references, hlock->pin_count))
+			return 1;
+	return 0;
+}
+
 static int
 __lock_set_class(struct lockdep_map *lock, const char *name,
 		 struct lock_class_key *key, unsigned int subclass,
@@ -3494,15 +3511,8 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 	curr->lockdep_depth = i;
 	curr->curr_chain_key = hlock->prev_chain_key;
 
-	for (; i < depth; i++) {
-		hlock = curr->held_locks + i;
-		if (!__lock_acquire(hlock->instance,
-			hlock_class(hlock)->subclass, hlock->trylock,
-				hlock->read, hlock->check, hlock->hardirqs_off,
-				hlock->nest_lock, hlock->acquire_ip,
-				hlock->references, hlock->pin_count))
-			return 0;
-	}
+	if (validate_held_lock(curr, depth, i))
+		return 0;
 
 	/*
 	 * I took it apart and put it back together again, except now I have
@@ -3573,15 +3583,8 @@ __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
 	curr->lockdep_depth = i;
 	curr->curr_chain_key = hlock->prev_chain_key;
 
-	for (i++; i < depth; i++) {
-		hlock = curr->held_locks + i;
-		if (!__lock_acquire(hlock->instance,
-			hlock_class(hlock)->subclass, hlock->trylock,
-				hlock->read, hlock->check, hlock->hardirqs_off,
-				hlock->nest_lock, hlock->acquire_ip,
-				hlock->references, hlock->pin_count))
-			return 0;
-	}
+	if (validate_held_lock(curr, depth, i + 1))
+		return 0;
 
 	/*
 	 * We had N bottles of beer on the wall, we drank one, but now
-- 
2.1.4

Re: [PATCH 2/3] lockdep: consolidate by new validate_held_lock()

[Peter Zijlstra]

On Fri, Feb 03, 2017 at 01:38:16AM +0900, J. R. Okajima wrote:
> A simple consolidataion. The behaviour should not change.
> 
> Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
> ---
>  kernel/locking/lockdep.c | 39 +++++++++++++++++++++------------------
>  1 file changed, 21 insertions(+), 18 deletions(-)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index b7a2001..7dc8f8e 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -3464,6 +3464,23 @@ static struct held_lock *find_held_lock(struct task_struct *curr,
>  	return ret;
>  }
>  
> +static int validate_held_lock(struct task_struct *curr, unsigned int depth,
> +			      int idx)
> +{
> +	struct held_lock *hlock;
> +
> +	for (hlock = curr->held_locks + idx; idx < depth; idx++, hlock++)
> +		if (!__lock_acquire(hlock->instance,
> +				    hlock_class(hlock)->subclass,
> +				    hlock->trylock,
> +				    hlock->read, hlock->check,
> +				    hlock->hardirqs_off,
> +				    hlock->nest_lock, hlock->acquire_ip,
> +				    hlock->references, hlock->pin_count))
> +			return 1;
> +	return 0;
> +}

I added the extra { } required by coding style and renamed the function
to reacquire_held_locks().

Plural because it has the loop, and reacquire because that is what it
does. Alternatively 'rebuild' is also possible if someone really doesn't
like reacquire.

[tip:locking/core] locking/lockdep: Factor out the validate_held_lock() helper function

[tip-bot for J. R. Okajima]

Commit-ID:  e969970be033841d4c16b2e8ec8a3608347db861
Gitweb:     http://git.kernel.org/tip/e969970be033841d4c16b2e8ec8a3608347db861
Author:     J. R. Okajima <hooanon05g@gmail.com>
AuthorDate: Fri, 3 Feb 2017 01:38:16 +0900
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 16 Mar 2017 09:57:07 +0100

locking/lockdep: Factor out the validate_held_lock() helper function

Behaviour should not change.

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1486053497-9948-2-git-send-email-hooanon05g@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/locking/lockdep.c | 40 ++++++++++++++++++++++------------------
 1 file changed, 22 insertions(+), 18 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 0d28b82..da79548 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3473,6 +3473,24 @@ out:
 	return ret;
 }
 
+static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
+			      int idx)
+{
+	struct held_lock *hlock;
+
+	for (hlock = curr->held_locks + idx; idx < depth; idx++, hlock++) {
+		if (!__lock_acquire(hlock->instance,
+				    hlock_class(hlock)->subclass,
+				    hlock->trylock,
+				    hlock->read, hlock->check,
+				    hlock->hardirqs_off,
+				    hlock->nest_lock, hlock->acquire_ip,
+				    hlock->references, hlock->pin_count))
+			return 1;
+	}
+	return 0;
+}
+
 static int
 __lock_set_class(struct lockdep_map *lock, const char *name,
 		 struct lock_class_key *key, unsigned int subclass,
@@ -3503,15 +3521,8 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 	curr->lockdep_depth = i;
 	curr->curr_chain_key = hlock->prev_chain_key;
 
-	for (; i < depth; i++) {
-		hlock = curr->held_locks + i;
-		if (!__lock_acquire(hlock->instance,
-			hlock_class(hlock)->subclass, hlock->trylock,
-				hlock->read, hlock->check, hlock->hardirqs_off,
-				hlock->nest_lock, hlock->acquire_ip,
-				hlock->references, hlock->pin_count))
-			return 0;
-	}
+	if (reacquire_held_locks(curr, depth, i))
+		return 0;
 
 	/*
 	 * I took it apart and put it back together again, except now I have
@@ -3582,15 +3593,8 @@ __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
 	curr->lockdep_depth = i;
 	curr->curr_chain_key = hlock->prev_chain_key;
 
-	for (i++; i < depth; i++) {
-		hlock = curr->held_locks + i;
-		if (!__lock_acquire(hlock->instance,
-			hlock_class(hlock)->subclass, hlock->trylock,
-				hlock->read, hlock->check, hlock->hardirqs_off,
-				hlock->nest_lock, hlock->acquire_ip,
-				hlock->references, hlock->pin_count))
-			return 0;
-	}
+	if (reacquire_held_locks(curr, depth, i + 1))
+		return 0;
 
 	/*
 	 * We had N bottles of beer on the wall, we drank one, but now

[PATCH 3/3] lockdep: new annotation lock_downgrade()

[J. R. Okajima]

The commit
	f831948 2016-11-30 locking/lockdep: Provide a type check for lock_is_held
didn't fully support rwsem. Here downgrade_write() supports the added type.

Originally-written-by: Peter Zijlstra <peterz@infradead.org>
See-also: http://marc.info/?l=linux-kernel&m=148581164003149&w=2
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
---
 include/linux/lockdep.h  |  2 ++
 kernel/locking/lockdep.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/locking/rwsem.c   |  6 ++----
 3 files changed, 59 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 0345cbf..22f304c 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -361,6 +361,8 @@ static inline void lock_set_subclass(struct lockdep_map *lock,
 	lock_set_class(lock, lock->name, lock->key, subclass, ip);
 }
 
+extern void lock_downgrade(struct lockdep_map *lock, unsigned long ip);
+
 extern void lockdep_set_current_reclaim_state(gfp_t gfp_mask);
 extern void lockdep_clear_current_reclaim_state(void);
 extern void lockdep_trace_alloc(gfp_t mask);
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7dc8f8e..6a4a740 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3523,6 +3523,44 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 	return 1;
 }
 
+static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
+{
+	struct task_struct *curr = current;
+	struct held_lock *hlock;
+	unsigned int depth;
+	int i;
+
+	depth = curr->lockdep_depth;
+	/*
+	 * This function is about (re)setting the class of a held lock,
+	 * yet we're not actually holding any locks. Naughty user!
+	 */
+	if (DEBUG_LOCKS_WARN_ON(!depth))
+		return 0;
+
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock)
+		return print_unlock_imbalance_bug(curr, lock, ip);
+
+	curr->lockdep_depth = i;
+	curr->curr_chain_key = hlock->prev_chain_key;
+
+	WARN(hlock->read, "downgrading a read lock");
+	hlock->read = 1;
+	hlock->acquire_ip = ip;
+
+	if (validate_held_lock(curr, depth, i))
+		return 0;
+
+	/*
+	 * I took it apart and put it back together again, except now I have
+	 * these 'spare' parts.. where shall I put them.
+	 */
+	if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
+		return 0;
+	return 1;
+}
+
 /*
  * Remove the lock to the list of currently held locks - this gets
  * called on mutex_unlock()/spin_unlock*() (or on a failed
@@ -3749,6 +3787,23 @@ void lock_set_class(struct lockdep_map *lock, const char *name,
 }
 EXPORT_SYMBOL_GPL(lock_set_class);
 
+void lock_downgrade(struct lockdep_map *lock, unsigned long ip)
+{
+	unsigned long flags;
+
+	if (unlikely(current->lockdep_recursion))
+		return;
+
+	raw_local_irq_save(flags);
+	current->lockdep_recursion = 1;
+	check_flags(flags);
+	if (__lock_downgrade(lock, ip))
+		check_chain_key(current);
+	current->lockdep_recursion = 0;
+	raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lock_downgrade);
+
 /*
  * We are not always called with irqs disabled - do that here,
  * and also avoid lockdep recursion:
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 45ba475..31db3ef 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -123,10 +123,8 @@ EXPORT_SYMBOL(up_write);
  */
 void downgrade_write(struct rw_semaphore *sem)
 {
-	/*
-	 * lockdep: a downgraded write will live on as a write
-	 * dependency.
-	 */
+	lock_downgrade(&sem->dep_map, _RET_IP_);
+
 	rwsem_set_reader_owned(sem);
 	__downgrade_write(sem);
 }
-- 
2.1.4

Re: [PATCH 3/3] lockdep: new annotation lock_downgrade()

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1508 bytes --]

Hi Okajima,

[auto build test ERROR on tip/locking/core]
[also build test ERROR on v4.10-rc6 next-20170202]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/J-R-Okajima/lockdep-consolidate-by-new-find_held_lock/20170203-010303
config: x86_64-randconfig-x018-201705 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   kernel/locking/rwsem.c: In function 'downgrade_write':
>> kernel/locking/rwsem.c:126:2: error: implicit declaration of function 'lock_downgrade' [-Werror=implicit-function-declaration]
     lock_downgrade(&sem->dep_map, _RET_IP_);
     ^~~~~~~~~~~~~~
>> kernel/locking/rwsem.c:126:21: error: 'struct rw_semaphore' has no member named 'dep_map'
     lock_downgrade(&sem->dep_map, _RET_IP_);
                        ^~
   cc1: some warnings being treated as errors

vim +/lock_downgrade +126 kernel/locking/rwsem.c

   120	
   121	/*
   122	 * downgrade write lock to read lock
   123	 */
   124	void downgrade_write(struct rw_semaphore *sem)
   125	{
 > 126		lock_downgrade(&sem->dep_map, _RET_IP_);
   127	
   128		rwsem_set_reader_owned(sem);
   129		__downgrade_write(sem);

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 22012 bytes --]

Re: [PATCH 3/3] lockdep: new annotation lock_downgrade()

[Peter Zijlstra]

On Fri, Feb 03, 2017 at 01:59:37AM +0800, kbuild test robot wrote:
> Hi Okajima,
> 
> [auto build test ERROR on tip/locking/core]
> [also build test ERROR on v4.10-rc6 next-20170202]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> 
> url:    https://github.com/0day-ci/linux/commits/J-R-Okajima/lockdep-consolidate-by-new-find_held_lock/20170203-010303
> config: x86_64-randconfig-x018-201705 (attached as .config)
> compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
> reproduce:
>         # save the attached .config to linux build tree
>         make ARCH=x86_64 
> 
> All errors (new ones prefixed by >>):
> 
>    kernel/locking/rwsem.c: In function 'downgrade_write':
> >> kernel/locking/rwsem.c:126:2: error: implicit declaration of function 'lock_downgrade' [-Werror=implicit-function-declaration]
>      lock_downgrade(&sem->dep_map, _RET_IP_);
>      ^~~~~~~~~~~~~~
> >> kernel/locking/rwsem.c:126:21: error: 'struct rw_semaphore' has no member named 'dep_map'
>      lock_downgrade(&sem->dep_map, _RET_IP_);
>                         ^~
>    cc1: some warnings being treated as errors
> 
> vim +/lock_downgrade +126 kernel/locking/rwsem.c
> 
>    120	
>    121	/*
>    122	 * downgrade write lock to read lock
>    123	 */
>    124	void downgrade_write(struct rw_semaphore *sem)
>    125	{
>  > 126		lock_downgrade(&sem->dep_map, _RET_IP_);
>    127	
>    128		rwsem_set_reader_owned(sem);
>    129		__downgrade_write(sem);

This is what you need !LOCKDEP stubs for ;-)

Re: [PATCH 3/3] lockdep: new annotation lock_downgrade()

[J. R. Okajima]

Peter Zijlstra:
> > >> kernel/locking/rwsem.c:126:2: error: implicit declaration of functi=
on 'lock_downgrade' [-Werror=3Dimplicit-function-declaration]
> >      lock_downgrade(&sem->dep_map, _RET_IP_);
> >      ^~~~~~~~~~~~~~
	:::
> This is what you need !LOCKDEP stubs for ;-)

Ok, here is the update.
Just one line added.


J. R. Okajima


commit 6874cbfb3c4f757efecbeb800bfd4db1050698f6
Author: J. R. Okajima <hooanon05g@gmail.com>
Date:   Thu Feb 2 23:41:38 2017 +0900

    lockdep: new annotation lock_downgrade()
    =

    The commit
    	f831948 2016-11-30 locking/lockdep: Provide a type check for lock_is_=
held
    didn't fully support rwsem. Here downgrade_write() supports the added =
type.
    =

    Originally-written-by: Peter Zijlstra <peterz@infradead.org>
    See-also: http://marc.info/?l=3Dlinux-kernel&m=3D148581164003149&w=3D2
    Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 0345cbf..ba75d06 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -361,6 +361,8 @@ static inline void lock_set_subclass(struct lockdep_ma=
p *lock,
 	lock_set_class(lock, lock->name, lock->key, subclass, ip);
 }
 =

+extern void lock_downgrade(struct lockdep_map *lock, unsigned long ip);
+
 extern void lockdep_set_current_reclaim_state(gfp_t gfp_mask);
 extern void lockdep_clear_current_reclaim_state(void);
 extern void lockdep_trace_alloc(gfp_t mask);
@@ -413,6 +415,7 @@ static inline void lockdep_on(void)
 =

 # define lock_acquire(l, s, t, r, c, n, i)	do { } while (0)
 # define lock_release(l, n, i)			do { } while (0)
+# define lock_downgrade(l, i)			do { } while (0)
 # define lock_set_class(l, n, k, s, i)		do { } while (0)
 # define lock_set_subclass(l, s, i)		do { } while (0)
 # define lockdep_set_current_reclaim_state(g)	do { } while (0)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7dc8f8e..6a4a740 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3523,6 +3523,44 @@ __lock_set_class(struct lockdep_map *lock, const ch=
ar *name,
 	return 1;
 }
 =

+static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
+{
+	struct task_struct *curr =3D current;
+	struct held_lock *hlock;
+	unsigned int depth;
+	int i;
+
+	depth =3D curr->lockdep_depth;
+	/*
+	 * This function is about (re)setting the class of a held lock,
+	 * yet we're not actually holding any locks. Naughty user!
+	 */
+	if (DEBUG_LOCKS_WARN_ON(!depth))
+		return 0;
+
+	hlock =3D find_held_lock(curr, lock, depth, &i);
+	if (!hlock)
+		return print_unlock_imbalance_bug(curr, lock, ip);
+
+	curr->lockdep_depth =3D i;
+	curr->curr_chain_key =3D hlock->prev_chain_key;
+
+	WARN(hlock->read, "downgrading a read lock");
+	hlock->read =3D 1;
+	hlock->acquire_ip =3D ip;
+
+	if (validate_held_lock(curr, depth, i))
+		return 0;
+
+	/*
+	 * I took it apart and put it back together again, except now I have
+	 * these 'spare' parts.. where shall I put them.
+	 */
+	if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth !=3D depth))
+		return 0;
+	return 1;
+}
+
 /*
  * Remove the lock to the list of currently held locks - this gets
  * called on mutex_unlock()/spin_unlock*() (or on a failed
@@ -3749,6 +3787,23 @@ void lock_set_class(struct lockdep_map *lock, const=
 char *name,
 }
 EXPORT_SYMBOL_GPL(lock_set_class);
 =

+void lock_downgrade(struct lockdep_map *lock, unsigned long ip)
+{
+	unsigned long flags;
+
+	if (unlikely(current->lockdep_recursion))
+		return;
+
+	raw_local_irq_save(flags);
+	current->lockdep_recursion =3D 1;
+	check_flags(flags);
+	if (__lock_downgrade(lock, ip))
+		check_chain_key(current);
+	current->lockdep_recursion =3D 0;
+	raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lock_downgrade);
+
 /*
  * We are not always called with irqs disabled - do that here,
  * and also avoid lockdep recursion:
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 45ba475..31db3ef 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -123,10 +123,8 @@ EXPORT_SYMBOL(up_write);
  */
 void downgrade_write(struct rw_semaphore *sem)
 {
-	/*
-	 * lockdep: a downgraded write will live on as a write
-	 * dependency.
-	 */
+	lock_downgrade(&sem->dep_map, _RET_IP_);
+
 	rwsem_set_reader_owned(sem);
 	__downgrade_write(sem);
 }

Re: [PATCH 3/3] lockdep: new annotation lock_downgrade()

[Peter Zijlstra]

On Fri, Feb 03, 2017 at 06:05:31AM +0900, J. R. Okajima wrote:
> Peter Zijlstra:
> > > >> kernel/locking/rwsem.c:126:2: error: implicit declaration of functi=
> on 'lock_downgrade' [-Werror=3Dimplicit-function-declaration]
> > >      lock_downgrade(&sem->dep_map, _RET_IP_);
> > >      ^~~~~~~~~~~~~~
> 	:::
> > This is what you need !LOCKDEP stubs for ;-)
> 
> Ok, here is the update.
> Just one line added.

Thanks!

(this version was white-space mangled but I took the old one and added
the one line).

[tip:locking/core] locking/lockdep: Add new check to lock_downgrade()

[tip-bot for J. R. Okajima]

Commit-ID:  6419c4af777a773a45a1b1af735de0fcd9a7dcc7
Gitweb:     http://git.kernel.org/tip/6419c4af777a773a45a1b1af735de0fcd9a7dcc7
Author:     J. R. Okajima <hooanon05g@gmail.com>
AuthorDate: Fri, 3 Feb 2017 01:38:17 +0900
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 16 Mar 2017 09:57:07 +0100

locking/lockdep: Add new check to lock_downgrade()

Commit:

  f8319483f57f ("locking/lockdep: Provide a type check for lock_is_held")

didn't fully cover rwsems as downgrade_write() was left out.

Introduce lock_downgrade() and use it to add new checks.

See-also: http://marc.info/?l=linux-kernel&m=148581164003149&w=2
Originally-written-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1486053497-9948-3-git-send-email-hooanon05g@gmail.com
[ Rewrote the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/lockdep.h  |  3 +++
 kernel/locking/lockdep.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/locking/rwsem.c   |  6 ++----
 3 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 1e327bb..fffe49f 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -361,6 +361,8 @@ static inline void lock_set_subclass(struct lockdep_map *lock,
 	lock_set_class(lock, lock->name, lock->key, subclass, ip);
 }
 
+extern void lock_downgrade(struct lockdep_map *lock, unsigned long ip);
+
 extern void lockdep_set_current_reclaim_state(gfp_t gfp_mask);
 extern void lockdep_clear_current_reclaim_state(void);
 extern void lockdep_trace_alloc(gfp_t mask);
@@ -411,6 +413,7 @@ static inline void lockdep_on(void)
 
 # define lock_acquire(l, s, t, r, c, n, i)	do { } while (0)
 # define lock_release(l, n, i)			do { } while (0)
+# define lock_downgrade(l, i)			do { } while (0)
 # define lock_set_class(l, n, k, s, i)		do { } while (0)
 # define lock_set_subclass(l, s, i)		do { } while (0)
 # define lockdep_set_current_reclaim_state(g)	do { } while (0)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index da79548..b1a1cef 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3533,6 +3533,44 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 	return 1;
 }
 
+static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
+{
+	struct task_struct *curr = current;
+	struct held_lock *hlock;
+	unsigned int depth;
+	int i;
+
+	depth = curr->lockdep_depth;
+	/*
+	 * This function is about (re)setting the class of a held lock,
+	 * yet we're not actually holding any locks. Naughty user!
+	 */
+	if (DEBUG_LOCKS_WARN_ON(!depth))
+		return 0;
+
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock)
+		return print_unlock_imbalance_bug(curr, lock, ip);
+
+	curr->lockdep_depth = i;
+	curr->curr_chain_key = hlock->prev_chain_key;
+
+	WARN(hlock->read, "downgrading a read lock");
+	hlock->read = 1;
+	hlock->acquire_ip = ip;
+
+	if (reacquire_held_locks(curr, depth, i))
+		return 0;
+
+	/*
+	 * I took it apart and put it back together again, except now I have
+	 * these 'spare' parts.. where shall I put them.
+	 */
+	if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
+		return 0;
+	return 1;
+}
+
 /*
  * Remove the lock to the list of currently held locks - this gets
  * called on mutex_unlock()/spin_unlock*() (or on a failed
@@ -3759,6 +3797,23 @@ void lock_set_class(struct lockdep_map *lock, const char *name,
 }
 EXPORT_SYMBOL_GPL(lock_set_class);
 
+void lock_downgrade(struct lockdep_map *lock, unsigned long ip)
+{
+	unsigned long flags;
+
+	if (unlikely(current->lockdep_recursion))
+		return;
+
+	raw_local_irq_save(flags);
+	current->lockdep_recursion = 1;
+	check_flags(flags);
+	if (__lock_downgrade(lock, ip))
+		check_chain_key(current);
+	current->lockdep_recursion = 0;
+	raw_local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(lock_downgrade);
+
 /*
  * We are not always called with irqs disabled - do that here,
  * and also avoid lockdep recursion:
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 90a74cc..4d48b1c 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -124,10 +124,8 @@ EXPORT_SYMBOL(up_write);
  */
 void downgrade_write(struct rw_semaphore *sem)
 {
-	/*
-	 * lockdep: a downgraded write will live on as a write
-	 * dependency.
-	 */
+	lock_downgrade(&sem->dep_map, _RET_IP_);
+
 	rwsem_set_reader_owned(sem);
 	__downgrade_write(sem);
 }

[tip:locking/core] locking/lockdep: Factor out the find_held_lock() helper function

[tip-bot for J. R. Okajima]

Commit-ID:  41c2c5b86a5e1a691ddacfc03b631b87a0b19043
Gitweb:     http://git.kernel.org/tip/41c2c5b86a5e1a691ddacfc03b631b87a0b19043
Author:     J. R. Okajima <hooanon05g@gmail.com>
AuthorDate: Fri, 3 Feb 2017 01:38:15 +0900
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 16 Mar 2017 09:57:06 +0100

locking/lockdep: Factor out the find_held_lock() helper function

A simple consolidataion to factor out repeated patterns.

The behaviour should not change.

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1486053497-9948-1-git-send-email-hooanon05g@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/locking/lockdep.c | 114 ++++++++++++++++++++++-------------------------
 1 file changed, 54 insertions(+), 60 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index a95e5d1..0d28b82 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3437,13 +3437,49 @@ static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
 	return 0;
 }
 
+/* @depth must not be zero */
+static struct held_lock *find_held_lock(struct task_struct *curr,
+					struct lockdep_map *lock,
+					unsigned int depth, int *idx)
+{
+	struct held_lock *ret, *hlock, *prev_hlock;
+	int i;
+
+	i = depth - 1;
+	hlock = curr->held_locks + i;
+	ret = hlock;
+	if (match_held_lock(hlock, lock))
+		goto out;
+
+	ret = NULL;
+	for (i--, prev_hlock = hlock--;
+	     i >= 0;
+	     i--, prev_hlock = hlock--) {
+		/*
+		 * We must not cross into another context:
+		 */
+		if (prev_hlock->irq_context != hlock->irq_context) {
+			ret = NULL;
+			break;
+		}
+		if (match_held_lock(hlock, lock)) {
+			ret = hlock;
+			break;
+		}
+	}
+
+out:
+	*idx = i;
+	return ret;
+}
+
 static int
 __lock_set_class(struct lockdep_map *lock, const char *name,
 		 struct lock_class_key *key, unsigned int subclass,
 		 unsigned long ip)
 {
 	struct task_struct *curr = current;
-	struct held_lock *hlock, *prev_hlock;
+	struct held_lock *hlock;
 	struct lock_class *class;
 	unsigned int depth;
 	int i;
@@ -3456,21 +3492,10 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 	if (DEBUG_LOCKS_WARN_ON(!depth))
 		return 0;
 
-	prev_hlock = NULL;
-	for (i = depth-1; i >= 0; i--) {
-		hlock = curr->held_locks + i;
-		/*
-		 * We must not cross into another context:
-		 */
-		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
-			break;
-		if (match_held_lock(hlock, lock))
-			goto found_it;
-		prev_hlock = hlock;
-	}
-	return print_unlock_imbalance_bug(curr, lock, ip);
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock)
+		return print_unlock_imbalance_bug(curr, lock, ip);
 
-found_it:
 	lockdep_init_map(lock, name, key, 0);
 	class = register_lock_class(lock, subclass, 0);
 	hlock->class_idx = class - lock_classes + 1;
@@ -3508,7 +3533,7 @@ static int
 __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
 {
 	struct task_struct *curr = current;
-	struct held_lock *hlock, *prev_hlock;
+	struct held_lock *hlock;
 	unsigned int depth;
 	int i;
 
@@ -3527,21 +3552,10 @@ __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
 	 * Check whether the lock exists in the current stack
 	 * of held locks:
 	 */
-	prev_hlock = NULL;
-	for (i = depth-1; i >= 0; i--) {
-		hlock = curr->held_locks + i;
-		/*
-		 * We must not cross into another context:
-		 */
-		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
-			break;
-		if (match_held_lock(hlock, lock))
-			goto found_it;
-		prev_hlock = hlock;
-	}
-	return print_unlock_imbalance_bug(curr, lock, ip);
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock)
+		return print_unlock_imbalance_bug(curr, lock, ip);
 
-found_it:
 	if (hlock->instance == lock)
 		lock_release_holdtime(hlock);
 
@@ -3903,7 +3917,7 @@ static void
 __lock_contended(struct lockdep_map *lock, unsigned long ip)
 {
 	struct task_struct *curr = current;
-	struct held_lock *hlock, *prev_hlock;
+	struct held_lock *hlock;
 	struct lock_class_stats *stats;
 	unsigned int depth;
 	int i, contention_point, contending_point;
@@ -3916,22 +3930,12 @@ __lock_contended(struct lockdep_map *lock, unsigned long ip)
 	if (DEBUG_LOCKS_WARN_ON(!depth))
 		return;
 
-	prev_hlock = NULL;
-	for (i = depth-1; i >= 0; i--) {
-		hlock = curr->held_locks + i;
-		/*
-		 * We must not cross into another context:
-		 */
-		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
-			break;
-		if (match_held_lock(hlock, lock))
-			goto found_it;
-		prev_hlock = hlock;
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock) {
+		print_lock_contention_bug(curr, lock, ip);
+		return;
 	}
-	print_lock_contention_bug(curr, lock, ip);
-	return;
 
-found_it:
 	if (hlock->instance != lock)
 		return;
 
@@ -3955,7 +3959,7 @@ static void
 __lock_acquired(struct lockdep_map *lock, unsigned long ip)
 {
 	struct task_struct *curr = current;
-	struct held_lock *hlock, *prev_hlock;
+	struct held_lock *hlock;
 	struct lock_class_stats *stats;
 	unsigned int depth;
 	u64 now, waittime = 0;
@@ -3969,22 +3973,12 @@ __lock_acquired(struct lockdep_map *lock, unsigned long ip)
 	if (DEBUG_LOCKS_WARN_ON(!depth))
 		return;
 
-	prev_hlock = NULL;
-	for (i = depth-1; i >= 0; i--) {
-		hlock = curr->held_locks + i;
-		/*
-		 * We must not cross into another context:
-		 */
-		if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
-			break;
-		if (match_held_lock(hlock, lock))
-			goto found_it;
-		prev_hlock = hlock;
+	hlock = find_held_lock(curr, lock, depth, &i);
+	if (!hlock) {
+		print_lock_contention_bug(curr, lock, _RET_IP_);
+		return;
 	}
-	print_lock_contention_bug(curr, lock, _RET_IP_);
-	return;
 
-found_it:
 	if (hlock->instance != lock)
 		return;