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-rw-r--r--kernel/futex.c23
1 files changed, 20 insertions, 3 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 0518a0bfc746..ca5bb9cba5cf 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -903,11 +903,27 @@ void exit_pi_state_list(struct task_struct *curr)
*/
raw_spin_lock_irq(&curr->pi_lock);
while (!list_empty(head)) {
-
next = head->next;
pi_state = list_entry(next, struct futex_pi_state, list);
key = pi_state->key;
hb = hash_futex(&key);
+
+ /*
+ * We can race against put_pi_state() removing itself from the
+ * list (a waiter going away). put_pi_state() will first
+ * decrement the reference count and then modify the list, so
+ * its possible to see the list entry but fail this reference
+ * acquire.
+ *
+ * In that case; drop the locks to let put_pi_state() make
+ * progress and retry the loop.
+ */
+ if (!atomic_inc_not_zero(&pi_state->refcount)) {
+ raw_spin_unlock_irq(&curr->pi_lock);
+ cpu_relax();
+ raw_spin_lock_irq(&curr->pi_lock);
+ continue;
+ }
raw_spin_unlock_irq(&curr->pi_lock);
spin_lock(&hb->lock);
@@ -918,8 +934,10 @@ void exit_pi_state_list(struct task_struct *curr)
* task still owns the PI-state:
*/
if (head->next != next) {
+ /* retain curr->pi_lock for the loop invariant */
raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);
+ put_pi_state(pi_state);
continue;
}
@@ -927,9 +945,8 @@ void exit_pi_state_list(struct task_struct *curr)
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
pi_state->owner = NULL;
- raw_spin_unlock(&curr->pi_lock);
- get_pi_state(pi_state);
+ raw_spin_unlock(&curr->pi_lock);
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);