@@ -2227,30 +2227,34 @@ static void unqueue_me_pi(struct futex_q *q)
spin_unlock(q->lock_ptr);
}
-/*
- * Fixup the pi_state owner with the new owner.
- *
- * Must be called with hash bucket lock held and mm->sem held for non
- * private futexes.
- */
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
- struct task_struct *newowner)
+ struct task_struct *argowner)
{
- u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
struct futex_pi_state *pi_state = q->pi_state;
- struct task_struct *oldowner = pi_state->owner;
u32 uval, uninitialized_var(curval), newval;
+ struct task_struct *oldowner, *newowner;
+ u32 newtid;
int ret;
+ lockdep_assert_held(q->lock_ptr);
+
+ oldowner = pi_state->owner;
/* Owner died? */
if (!pi_state->owner)
newtid |= FUTEX_OWNER_DIED;
/*
- * We are here either because we stole the rtmutex from the
- * previous highest priority waiter or we are the highest priority
- * waiter but failed to get the rtmutex the first time.
- * We have to replace the newowner TID in the user space variable.
+ * We are here because either:
+ *
+ * - we stole the lock and pi_state->owner needs updating to reflect
+ * that (@argowner == current),
+ *
+ * or:
+ *
+ * - someone stole our lock and we need to fix things to point to the
+ * new owner (@argowner == NULL).
+ *
+ * Either way, we have to replace the TID in the user space variable.
* This must be atomic as we have to preserve the owner died bit here.
*
* Note: We write the user space value _before_ changing the pi_state
@@ -2264,6 +2268,39 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
* in lookup_pi_state.
*/
retry:
+ if (!argowner) {
+ if (oldowner != current) {
+ /*
+ * We raced against a concurrent self; things are
+ * already fixed up. Nothing to do.
+ */
+ return 0;
+ }
+
+ if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
+ /* We got the lock after all, nothing to fix. */
+ return 0;
+ }
+
+ /*
+ * Since we just failed the trylock; there must be an owner.
+ */
+ newowner = rt_mutex_owner(&pi_state->pi_mutex);
+ BUG_ON(!newowner);
+ } else {
+ WARN_ON_ONCE(argowner != current);
+ if (oldowner == current) {
+ /*
+ * We raced against a concurrent self; things are
+ * already fixed up. Nothing to do.
+ */
+ return 0;
+ }
+ newowner = argowner;
+ }
+
+ newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
+
if (get_futex_value_locked(&uval, uaddr))
goto handle_fault;
@@ -2350,12 +2387,29 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
/*
* Got the lock. We might not be the anticipated owner if we
* did a lock-steal - fix up the PI-state in that case:
+ *
+ * Speculative pi_state->owner read (we don't hold wait_lock);
+ * since we own the lock pi_state->owner == current is the
+ * stable state, anything else needs more attention.
*/
if (q->pi_state->owner != current)
ret = fixup_pi_state_owner(uaddr, q, current);
goto out;
}
+ /*
+ * If we didn't get the lock; check if anybody stole it from us. In
+ * that case, we need to fix up the uval to point to them instead of
+ * us, otherwise bad things happen. [10]
+ *
+ * Another speculative read; pi_state->owner == current is unstable
+ * but needs our attention.
+ */
+ if (q->pi_state->owner == current) {
+ ret = fixup_pi_state_owner(uaddr, q, NULL);
+ goto out;
+ }
+
/*
* Paranoia check. If we did not take the lock, then we should not be
* the owner of the rt_mutex.
@@ -1284,6 +1284,19 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
return ret;
}
+static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
+{
+ int ret = try_to_take_rt_mutex(lock, current, NULL);
+
+ /*
+ * try_to_take_rt_mutex() sets the lock waiters bit
+ * unconditionally. Clean this up.
+ */
+ fixup_rt_mutex_waiters(lock);
+
+ return ret;
+}
+
/*
* Slow path try-lock function:
*/
@@ -1305,13 +1318,7 @@ static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
*/
raw_spin_lock(&lock->wait_lock);
- ret = try_to_take_rt_mutex(lock, current, NULL);
-
- /*
- * try_to_take_rt_mutex() sets the lock waiters bit
- * unconditionally. Clean this up.
- */
- fixup_rt_mutex_waiters(lock);
+ ret = __rt_mutex_slowtrylock(lock);
raw_spin_unlock(&lock->wait_lock);
@@ -1496,6 +1503,11 @@ int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
return rt_mutex_slowtrylock(lock);
}
+int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
+{
+ return __rt_mutex_slowtrylock(lock);
+}
+
/**
* rt_mutex_timed_lock - lock a rt_mutex interruptible
* the timeout structure is provided
@@ -113,6 +113,7 @@ extern bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter);
extern int rt_mutex_timed_futex_lock(struct rt_mutex *l, struct hrtimer_sleeper *to);
extern int rt_mutex_futex_trylock(struct rt_mutex *l);
+extern int __rt_mutex_futex_trylock(struct rt_mutex *l);
extern void rt_mutex_futex_unlock(struct rt_mutex *lock);
extern bool __rt_mutex_futex_unlock(struct rt_mutex *lock,