futex: Pull rt_mutex_futex_unlock() out from under hb->lock
There's a number of 'interesting' problems, all caused by holding hb->lock while doing the rt_mutex_unlock() equivalient. Notably: - a PI inversion on hb->lock; and, - a SCHED_DEADLINE crash because of pointer instability. The previous changes: - changed the locking rules to cover {uval,pi_state} with wait_lock. - allow to do rt_mutex_futex_unlock() without dropping wait_lock; which in turn allows to rely on wait_lock atomicity completely. - simplified the waiter conundrum. It's now sufficient to hold rtmutex::wait_lock and a reference on the pi_state to protect the state consistency, so hb->lock can be dropped before calling rt_mutex_futex_unlock(). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: juri.lelli@arm.com Cc: bigeasy@linutronix.de Cc: xlpang@redhat.com Cc: rostedt@goodmis.org Cc: mathieu.desnoyers@efficios.com Cc: jdesfossez@efficios.com Cc: dvhart@infradead.org Cc: bristot@redhat.com Link: http://lkml.kernel.org/r/20170322104151.900002056@infradead.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
parent
73d786bd04
commit
16ffa12d74
154
kernel/futex.c
154
kernel/futex.c
@ -921,10 +921,12 @@ void exit_pi_state_list(struct task_struct *curr)
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pi_state->owner = NULL;
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raw_spin_unlock_irq(&curr->pi_lock);
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rt_mutex_futex_unlock(&pi_state->pi_mutex);
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get_pi_state(pi_state);
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spin_unlock(&hb->lock);
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rt_mutex_futex_unlock(&pi_state->pi_mutex);
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put_pi_state(pi_state);
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raw_spin_lock_irq(&curr->pi_lock);
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}
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raw_spin_unlock_irq(&curr->pi_lock);
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@ -1037,6 +1039,11 @@ static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
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* has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
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* which in turn means that futex_lock_pi() still has a reference on
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* our pi_state.
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*
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* The waiter holding a reference on @pi_state also protects against
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* the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
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* and futex_wait_requeue_pi() as it cannot go to 0 and consequently
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* free pi_state before we can take a reference ourselves.
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*/
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WARN_ON(!atomic_read(&pi_state->refcount));
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@ -1380,48 +1387,40 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
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smp_store_release(&q->lock_ptr, NULL);
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}
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static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter,
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struct futex_hash_bucket *hb)
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/*
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* Caller must hold a reference on @pi_state.
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*/
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static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
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{
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struct task_struct *new_owner;
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struct futex_pi_state *pi_state = top_waiter->pi_state;
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u32 uninitialized_var(curval), newval;
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struct task_struct *new_owner;
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bool deboost = false;
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DEFINE_WAKE_Q(wake_q);
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bool deboost;
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int ret = 0;
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if (!pi_state)
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return -EINVAL;
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/*
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* If current does not own the pi_state then the futex is
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* inconsistent and user space fiddled with the futex value.
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*/
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if (pi_state->owner != current)
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return -EINVAL;
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raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
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new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
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/*
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* When we interleave with futex_lock_pi() where it does
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* rt_mutex_timed_futex_lock(), we might observe @this futex_q waiter,
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* but the rt_mutex's wait_list can be empty (either still, or again,
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* depending on which side we land).
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*
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* When this happens, give up our locks and try again, giving the
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* futex_lock_pi() instance time to complete, either by waiting on the
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* rtmutex or removing itself from the futex queue.
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*/
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if (!new_owner) {
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raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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return -EAGAIN;
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/*
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* Since we held neither hb->lock nor wait_lock when coming
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* into this function, we could have raced with futex_lock_pi()
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* such that we might observe @this futex_q waiter, but the
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* rt_mutex's wait_list can be empty (either still, or again,
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* depending on which side we land).
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*
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* When this happens, give up our locks and try again, giving
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* the futex_lock_pi() instance time to complete, either by
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* waiting on the rtmutex or removing itself from the futex
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* queue.
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*/
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ret = -EAGAIN;
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goto out_unlock;
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}
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/*
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* We pass it to the next owner. The WAITERS bit is always
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* kept enabled while there is PI state around. We cleanup the
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* owner died bit, because we are the owner.
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* We pass it to the next owner. The WAITERS bit is always kept
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* enabled while there is PI state around. We cleanup the owner
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* died bit, because we are the owner.
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*/
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newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
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@ -1444,10 +1443,8 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter
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ret = -EINVAL;
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}
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if (ret) {
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raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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return ret;
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}
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if (ret)
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goto out_unlock;
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raw_spin_lock(&pi_state->owner->pi_lock);
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WARN_ON(list_empty(&pi_state->list));
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@ -1465,15 +1462,15 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter
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*/
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deboost = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
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out_unlock:
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raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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spin_unlock(&hb->lock);
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if (deboost) {
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wake_up_q(&wake_q);
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rt_mutex_adjust_prio(current);
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}
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return 0;
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return ret;
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}
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/*
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@ -2232,7 +2229,8 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
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/*
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* We are here either because we stole the rtmutex from the
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* previous highest priority waiter or we are the highest priority
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* waiter but failed to get the rtmutex the first time.
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* waiter but have failed to get the rtmutex the first time.
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*
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* We have to replace the newowner TID in the user space variable.
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* This must be atomic as we have to preserve the owner died bit here.
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*
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@ -2249,7 +2247,7 @@ retry:
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if (get_futex_value_locked(&uval, uaddr))
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goto handle_fault;
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while (1) {
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for (;;) {
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newval = (uval & FUTEX_OWNER_DIED) | newtid;
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if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
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@ -2345,6 +2343,10 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
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/*
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* Got the lock. We might not be the anticipated owner if we
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* did a lock-steal - fix up the PI-state in that case:
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*
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* We can safely read pi_state->owner without holding wait_lock
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* because we now own the rt_mutex, only the owner will attempt
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* to change it.
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*/
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if (q->pi_state->owner != current)
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ret = fixup_pi_state_owner(uaddr, q, current);
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@ -2584,6 +2586,7 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
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ktime_t *time, int trylock)
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{
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struct hrtimer_sleeper timeout, *to = NULL;
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struct futex_pi_state *pi_state = NULL;
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struct futex_hash_bucket *hb;
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struct futex_q q = futex_q_init;
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int res, ret;
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@ -2670,12 +2673,19 @@ retry_private:
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* If fixup_owner() faulted and was unable to handle the fault, unlock
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* it and return the fault to userspace.
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*/
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if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
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rt_mutex_futex_unlock(&q.pi_state->pi_mutex);
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if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
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pi_state = q.pi_state;
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get_pi_state(pi_state);
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}
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/* Unqueue and drop the lock */
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unqueue_me_pi(&q);
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if (pi_state) {
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rt_mutex_futex_unlock(&pi_state->pi_mutex);
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put_pi_state(pi_state);
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}
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goto out_put_key;
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out_unlock_put_key:
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@ -2738,10 +2748,36 @@ retry:
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*/
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top_waiter = futex_top_waiter(hb, &key);
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if (top_waiter) {
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ret = wake_futex_pi(uaddr, uval, top_waiter, hb);
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struct futex_pi_state *pi_state = top_waiter->pi_state;
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ret = -EINVAL;
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if (!pi_state)
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goto out_unlock;
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/*
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* In case of success wake_futex_pi dropped the hash
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* bucket lock.
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* If current does not own the pi_state then the futex is
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* inconsistent and user space fiddled with the futex value.
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*/
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if (pi_state->owner != current)
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goto out_unlock;
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/*
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* Grab a reference on the pi_state and drop hb->lock.
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*
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* The reference ensures pi_state lives, dropping the hb->lock
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* is tricky.. wake_futex_pi() will take rt_mutex::wait_lock to
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* close the races against futex_lock_pi(), but in case of
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* _any_ fail we'll abort and retry the whole deal.
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*/
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get_pi_state(pi_state);
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spin_unlock(&hb->lock);
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ret = wake_futex_pi(uaddr, uval, pi_state);
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put_pi_state(pi_state);
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/*
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* Success, we're done! No tricky corner cases.
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*/
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if (!ret)
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goto out_putkey;
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@ -2756,7 +2792,6 @@ retry:
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* setting the FUTEX_WAITERS bit. Try again.
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*/
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if (ret == -EAGAIN) {
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spin_unlock(&hb->lock);
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put_futex_key(&key);
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goto retry;
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}
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@ -2764,7 +2799,7 @@ retry:
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* wake_futex_pi has detected invalid state. Tell user
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* space.
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*/
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goto out_unlock;
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goto out_putkey;
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}
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/*
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@ -2774,8 +2809,10 @@ retry:
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* preserve the WAITERS bit not the OWNER_DIED one. We are the
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* owner.
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*/
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if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
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if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) {
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spin_unlock(&hb->lock);
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goto pi_faulted;
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}
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/*
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* If uval has changed, let user space handle it.
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@ -2789,7 +2826,6 @@ out_putkey:
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return ret;
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pi_faulted:
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spin_unlock(&hb->lock);
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put_futex_key(&key);
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ret = fault_in_user_writeable(uaddr);
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@ -2893,6 +2929,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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u32 __user *uaddr2)
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{
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struct hrtimer_sleeper timeout, *to = NULL;
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struct futex_pi_state *pi_state = NULL;
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struct rt_mutex_waiter rt_waiter;
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struct futex_hash_bucket *hb;
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union futex_key key2 = FUTEX_KEY_INIT;
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@ -2977,8 +3014,10 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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if (q.pi_state && (q.pi_state->owner != current)) {
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spin_lock(q.lock_ptr);
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ret = fixup_pi_state_owner(uaddr2, &q, current);
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if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current)
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rt_mutex_futex_unlock(&q.pi_state->pi_mutex);
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if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
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pi_state = q.pi_state;
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get_pi_state(pi_state);
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}
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/*
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* Drop the reference to the pi state which
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* the requeue_pi() code acquired for us.
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@ -3017,13 +3056,20 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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* the fault, unlock the rt_mutex and return the fault to
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* userspace.
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*/
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if (ret && rt_mutex_owner(pi_mutex) == current)
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rt_mutex_futex_unlock(pi_mutex);
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if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
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pi_state = q.pi_state;
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get_pi_state(pi_state);
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}
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/* Unqueue and drop the lock. */
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unqueue_me_pi(&q);
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}
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if (pi_state) {
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rt_mutex_futex_unlock(&pi_state->pi_mutex);
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put_pi_state(pi_state);
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}
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if (ret == -EINTR) {
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/*
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* We've already been requeued, but cannot restart by calling
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