On PREEMPT_RT the futex hashbucket spinlock becomes 'sleeping' and rtmutex based. That causes a lockdep false positive because some of the futex functions invoke spin_unlock(&hb->lock) with the wait_lock of the rtmutex associated to the pi_futex held. spin_unlock() in turn takes wait_lock of the rtmutex on which the spinlock is based which makes lockdep notice a lock recursion. Give the futex/rtmutex wait_lock a separate key.
Unified · Split
| @@ -214,7 +214,19 @@ EXPORT_SYMBOL_GPL(__rt_mutex_init); · 213 unmodified lines | |||
| 214 | void __sched rt_mutex_init_proxy_locked(struct rt_mutex_base *lock, | 214 | void __sched rt_mutex_init_proxy_locked(struct rt_mutex_base *lock, |
| 215 | struct task_struct *proxy_owner) | 215 | struct task_struct *proxy_owner) |
| 216 | { | 216 | { |
| 217 | static struct lock_class_key pi_futex_key; | ||
| 218 | |||
| 217 | __rt_mutex_base_init(lock); | 219 | __rt_mutex_base_init(lock); |
| 220 | /* | ||
| 221 | * On PREEMPT_RT the futex hashbucket spinlock becomes 'sleeping' | ||
| 222 | * and rtmutex based. That causes a lockdep false positive, because | ||
| 223 | * some of the futex functions invoke spin_unlock(&hb->lock) with | ||
| 224 | * the wait_lock of the rtmutex associated to the pi_futex held. | ||
| 225 | * spin_unlock() in turn takes wait_lock of the rtmutex on which | ||
| 226 | * the spinlock is based, which makes lockdep notice a lock | ||
| 227 | * recursion. Give the futex/rtmutex wait_lock a separate key. | ||
| 228 | */ | ||
| 229 | lockdep_set_class(&lock->wait_lock, &pi_futex_key); | ||
| 218 | rt_mutex_set_owner(lock, proxy_owner); | 230 | rt_mutex_set_owner(lock, proxy_owner); |
| 219 | } | 231 | } |
| 220 | 232 | ||