The sequence
static DEFINE_WW_CLASS(test_ww_class);
struct ww_acquire_ctx ww_ctx;
struct ww_mutex ww_lock_a;
struct ww_mutex ww_lock_b;
struct ww_mutex ww_lock_c;
struct mutex lock_c;
ww_acquire_init(&ww_ctx, &test_ww_class);
ww_mutex_init(&ww_lock_a, &test_ww_class);
ww_mutex_init(&ww_lock_b, &test_ww_class);
ww_mutex_init(&ww_lock_c, &test_ww_class);
mutex_init(&lock_c);
ww_mutex_lock(&ww_lock_a, &ww_ctx);
mutex_lock(&lock_c);
ww_mutex_lock(&ww_lock_b, &ww_ctx);
ww_mutex_lock(&ww_lock_c, &ww_ctx);
mutex_unlock(&lock_c); (*)
ww_mutex_unlock(&ww_lock_c);
ww_mutex_unlock(&ww_lock_b);
ww_mutex_unlock(&ww_lock_a);
ww_acquire_fini(&ww_ctx); (**)
will trigger the following error in __lock_release() when calling
mutex_release() at **:
DEBUG_LOCKS_WARN_ON(depth <= 0)
The problem is that the hlock merging happening at * updates the
references for test_ww_class incorrectly to 3 whereas it should've
updated it to 4 (representing all the instances for ww_ctx and
ww_lock_[abc]).
Fix this by updating the references during merging correctly taking into
account that we can have non-zero references (both for the hlock that we
merge into another hlock or for the hlock we are merging into).
v2: (Peter)
- Rebase on latest upstream tree.
- Sanitize overflow check and hlock_references() helper.
Cc: Ville Syrjälä <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Imre Deak <[email protected]>
---
kernel/locking/lockdep.c | 22 ++++++++++++----------
1 file changed, 12 insertions(+), 10 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7a48649ce6bc..1aa6dff3c12c 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3638,6 +3638,11 @@ print_lock_nested_lock_not_held(struct task_struct *curr,
static int __lock_is_held(const struct lockdep_map *lock, int read);
+static inline int hlock_references(struct held_lock *hlock)
+{
+ return hlock->references ? : 1;
+}
+
/*
* This gets called for every mutex_lock*()/spin_lock*() operation.
* We maintain the dependency maps and validate the locking attempt:
@@ -3703,17 +3708,14 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
if (depth) {
hlock = curr->held_locks + depth - 1;
if (hlock->class_idx == class_idx && nest_lock) {
- if (hlock->references) {
- /*
- * Check: unsigned int references:12, overflow.
- */
- if (DEBUG_LOCKS_WARN_ON(hlock->references == (1 << 12)-1))
- return 0;
+ if (!references)
+ references++;
- hlock->references++;
- } else {
- hlock->references = 2;
- }
+ hlock->references = hlock_references(hlock) + references;
+
+ /* Overflow */
+ if (DEBUG_LOCKS_WARN_ON(hlock->references < references))
+ return 0;
return 2;
}
--
2.17.1