Commit 9de0c9bb authored by Boqun Feng's avatar Boqun Feng Committed by Peter Zijlstra
Browse files

lockdep: Support deadlock detection for recursive read locks in check_noncircular() 



Currently, lockdep only has limit support for deadlock detection for
recursive read locks.

This patch support deadlock detection for recursive read locks. The
basic idea is:

We are about to add dependency B -> A in to the dependency graph, we use
check_noncircular() to find whether we have a strong dependency path
A -> .. -> B so that we have a strong dependency circle (a closed strong
dependency path):

	 A -> .. -> B -> A

, which doesn't have two adjacent dependencies as -(*R)-> L -(S*)->.

Since A -> .. -> B is already a strong dependency path, so if either
B -> A is -(E*)-> or A -> .. -> B is -(*N)->, the circle A -> .. -> B ->
A is strong, otherwise not. So we introduce a new match function
hlock_conflict() to replace the class_equal() for the deadlock check in
check_noncircular().

Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-10-boqun.feng@gmail.com
parent 61775ed2

kernel/locking/lockdep.c

+35 −8
Original line number Diff line number Diff line
@@ -1838,6 +1838,33 @@ static inline bool class_equal(struct lock_list *entry, void *data) 
	return entry->class == data;

}



/*

 * We are about to add B -> A into the dependency graph, and in __bfs() a

 * strong dependency path A -> .. -> B is found: hlock_class equals

 * entry->class.

 *

 * We will have a deadlock case (conflict) if A -> .. -> B -> A is a strong

 * dependency cycle, that means:

 *

 * Either

 *

 *     a) B -> A is -(E*)->

 *

 * or

 *

 *     b) A -> .. -> B is -(*N)-> (i.e. A -> .. -(*N)-> B)

 *

 * as then we don't have -(*R)-> -(S*)-> in the cycle.

 */

static inline bool hlock_conflict(struct lock_list *entry, void *data)

{

	struct held_lock *hlock = (struct held_lock *)data;



	return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */

	       (hlock->read == 0 || /* B -> A is -(E*)-> */

		!entry->only_xr); /* A -> .. -> B is -(*N)-> */

}



static noinline void print_circular_bug(struct lock_list *this,

				struct lock_list *target,

				struct held_lock *check_src,
@@ -1950,13 +1977,13 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class) 
 * <target> or not.

 */

static noinline enum bfs_result

check_path(struct lock_class *target, struct lock_list *src_entry,

check_path(struct held_lock *target, struct lock_list *src_entry,

	   bool (*match)(struct lock_list *entry, void *data),

	   struct lock_list **target_entry)

{

	enum bfs_result ret;



	ret = __bfs_forwards(src_entry, (void *)target, class_equal,

			     target_entry);

	ret = __bfs_forwards(src_entry, target, match, target_entry);



	if (unlikely(bfs_error(ret)))

		print_bfs_bug(ret);
@@ -1983,7 +2010,7 @@ check_noncircular(struct held_lock *src, struct held_lock *target, 


	debug_atomic_inc(nr_cyclic_checks);



	ret = check_path(hlock_class(target), &src_entry, &target_entry);

	ret = check_path(target, &src_entry, hlock_conflict, &target_entry);



	if (unlikely(ret == BFS_RMATCH)) {

		if (!*trace) {
@@ -2021,7 +2048,7 @@ check_redundant(struct held_lock *src, struct held_lock *target) 


	debug_atomic_inc(nr_redundant_checks);



	ret = check_path(hlock_class(target), &src_entry, &target_entry);

	ret = check_path(target, &src_entry, class_equal, &target_entry);



	if (ret == BFS_RMATCH)

		debug_atomic_inc(nr_redundant);

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