Commit 0cce06ba authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

debugobjects,locking: Annotate debug_object_fill_pool() wait type violation 



There is an explicit wait-type violation in debug_object_fill_pool()
for PREEMPT_RT=n kernels which allows them to more easily fill the
object pool and reduce the chance of allocation failures.

Lockdep's wait-type checks are designed to check the PREEMPT_RT
locking rules even for PREEMPT_RT=n kernels and object to this, so
create a lockdep annotation to allow this to stand.

Specifically, create a 'lock' type that overrides the inner wait-type
while it is held -- allowing one to temporarily raise it, such that
the violation is hidden.

Reported-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reported-by: default avatarQi Zheng <zhengqi.arch@bytedance.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarQi Zheng <zhengqi.arch@bytedance.com>
Link: https://lkml.kernel.org/r/20230429100614.GA1489784@hirez.programming.kicks-ass.net
parent 0af462f1

include/linux/lockdep.h

+14 −0
Original line number Diff line number Diff line
@@ -339,6 +339,16 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie); 
#define lockdep_repin_lock(l,c)	lock_repin_lock(&(l)->dep_map, (c))

#define lockdep_unpin_lock(l,c)	lock_unpin_lock(&(l)->dep_map, (c))



/*

 * Must use lock_map_aquire_try() with override maps to avoid

 * lockdep thinking they participate in the block chain.

 */

#define DEFINE_WAIT_OVERRIDE_MAP(_name, _wait_type)	\

	struct lockdep_map _name = {			\

		.name = #_name "-wait-type-override",	\

		.wait_type_inner = _wait_type,		\

		.lock_type = LD_LOCK_WAIT_OVERRIDE, }



#else /* !CONFIG_LOCKDEP */



static inline void lockdep_init_task(struct task_struct *task)
@@ -427,6 +437,9 @@ extern int lockdep_is_held(const void *); 
#define lockdep_repin_lock(l, c)		do { (void)(l); (void)(c); } while (0)

#define lockdep_unpin_lock(l, c)		do { (void)(l); (void)(c); } while (0)



#define DEFINE_WAIT_OVERRIDE_MAP(_name, _wait_type)	\

	struct lockdep_map __maybe_unused _name = {}



#endif /* !LOCKDEP */



enum xhlock_context_t {
@@ -551,6 +564,7 @@ do { \ 
#define rwsem_release(l, i)			lock_release(l, i)



#define lock_map_acquire(l)			lock_acquire_exclusive(l, 0, 0, NULL, _THIS_IP_)

#define lock_map_acquire_try(l)			lock_acquire_exclusive(l, 0, 1, NULL, _THIS_IP_)

#define lock_map_acquire_read(l)		lock_acquire_shared_recursive(l, 0, 0, NULL, _THIS_IP_)

#define lock_map_acquire_tryread(l)		lock_acquire_shared_recursive(l, 0, 1, NULL, _THIS_IP_)

#define lock_map_release(l)			lock_release(l, _THIS_IP_)

include/linux/lockdep_types.h

+1 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ enum lockdep_wait_type { 
enum lockdep_lock_type {

	LD_LOCK_NORMAL = 0,	/* normal, catch all */

	LD_LOCK_PERCPU,		/* percpu */

	LD_LOCK_WAIT_OVERRIDE,	/* annotation */

	LD_LOCK_MAX,

};

kernel/locking/lockdep.c

+21 −7
Original line number Diff line number Diff line
@@ -2253,6 +2253,9 @@ static inline bool usage_match(struct lock_list *entry, void *mask) 


static inline bool usage_skip(struct lock_list *entry, void *mask)

{

	if (entry->class->lock_type == LD_LOCK_NORMAL)

		return false;



	/*

	 * Skip local_lock() for irq inversion detection.

	 *
@@ -2279,14 +2282,16 @@ static inline bool usage_skip(struct lock_list *entry, void *mask) 
	 * As a result, we will skip local_lock(), when we search for irq

	 * inversion bugs.

	 */

	if (entry->class->lock_type == LD_LOCK_PERCPU) {

		if (DEBUG_LOCKS_WARN_ON(entry->class->wait_type_inner < LD_WAIT_CONFIG))

	if (entry->class->lock_type == LD_LOCK_PERCPU &&

	    DEBUG_LOCKS_WARN_ON(entry->class->wait_type_inner < LD_WAIT_CONFIG))

		return false;



		return true;

	}

	/*

	 * Skip WAIT_OVERRIDE for irq inversion detection -- it's not actually

	 * a lock and only used to override the wait_type.

	 */



	return false;

	return true;

}



/*
@@ -4752,7 +4757,8 @@ static int check_wait_context(struct task_struct *curr, struct held_lock *next) 


	for (; depth < curr->lockdep_depth; depth++) {

		struct held_lock *prev = curr->held_locks + depth;

		u8 prev_inner = hlock_class(prev)->wait_type_inner;

		struct lock_class *class = hlock_class(prev);

		u8 prev_inner = class->wait_type_inner;



		if (prev_inner) {

			/*
@@ -4762,6 +4768,14 @@ static int check_wait_context(struct task_struct *curr, struct held_lock *next) 
			 * Also due to trylocks.

			 */

			curr_inner = min(curr_inner, prev_inner);



			/*

			 * Allow override for annotations -- this is typically

			 * only valid/needed for code that only exists when

			 * CONFIG_PREEMPT_RT=n.

			 */

			if (unlikely(class->lock_type == LD_LOCK_WAIT_OVERRIDE))

				curr_inner = prev_inner;

		}

	}

lib/debugobjects.c

+13 −2
Original line number Diff line number Diff line
@@ -591,10 +591,21 @@ static void debug_objects_fill_pool(void) 
{

	/*

	 * On RT enabled kernels the pool refill must happen in preemptible

	 * context:

	 * context -- for !RT kernels we rely on the fact that spinlock_t and

	 * raw_spinlock_t are basically the same type and this lock-type

	 * inversion works just fine.

	 */

	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible())

	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible()) {

		/*

		 * Annotate away the spinlock_t inside raw_spinlock_t warning

		 * by temporarily raising the wait-type to WAIT_SLEEP, matching

		 * the preemptible() condition above.

		 */

		static DEFINE_WAIT_OVERRIDE_MAP(fill_pool_map, LD_WAIT_SLEEP);

		lock_map_acquire_try(&fill_pool_map);

		fill_pool();

		lock_map_release(&fill_pool_map);

	}

}



static void