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futex: fixup unlocked requeue pi case
Thomas's testing caught a problem when the requeue target futex is unowned and multiple tasks are requeued to it. This patch ensures the FUTEX_WAITERS bit gets set if futex_requeue() will requeue one or more tasks in addition to the one acquiring the lock. Signed-off-by: Darren Hart <dvhltc@us.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@ -565,12 +565,14 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
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/**
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* futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
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* @uaddr: the pi futex user address
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* @hb: the pi futex hash bucket
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* @key: the futex key associated with uaddr and hb
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* @ps: the pi_state pointer where we store the result of the lookup
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* @task: the task to perform the atomic lock work for. This will be
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* "current" except in the case of requeue pi.
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* @uaddr: the pi futex user address
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* @hb: the pi futex hash bucket
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* @key: the futex key associated with uaddr and hb
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* @ps: the pi_state pointer where we store the result of the
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* lookup
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* @task: the task to perform the atomic lock work for. This will
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* be "current" except in the case of requeue pi.
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* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
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*
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* Returns:
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* 0 - ready to wait
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@ -582,7 +584,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
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static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
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union futex_key *key,
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struct futex_pi_state **ps,
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struct task_struct *task)
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struct task_struct *task, int set_waiters)
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{
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int lock_taken, ret, ownerdied = 0;
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u32 uval, newval, curval;
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@ -596,6 +598,8 @@ retry:
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* the locks. It will most likely not succeed.
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*/
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newval = task_pid_vnr(task);
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if (set_waiters)
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newval |= FUTEX_WAITERS;
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curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
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@ -1004,14 +1008,18 @@ void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key)
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/**
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* futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
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* @pifutex: the user address of the to futex
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* @hb1: the from futex hash bucket, must be locked by the caller
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* @hb2: the to futex hash bucket, must be locked by the caller
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* @key1: the from futex key
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* @key2: the to futex key
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* @pifutex: the user address of the to futex
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* @hb1: the from futex hash bucket, must be locked by the caller
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* @hb2: the to futex hash bucket, must be locked by the caller
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* @key1: the from futex key
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* @key2: the to futex key
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* @ps: address to store the pi_state pointer
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* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
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*
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* Try and get the lock on behalf of the top waiter if we can do it atomically.
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* Wake the top waiter if we succeed. hb1 and hb2 must be held by the caller.
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* Wake the top waiter if we succeed. If the caller specified set_waiters,
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* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
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* hb1 and hb2 must be held by the caller.
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*
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* Returns:
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* 0 - failed to acquire the lock atomicly
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@ -1022,15 +1030,23 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
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struct futex_hash_bucket *hb1,
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struct futex_hash_bucket *hb2,
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union futex_key *key1, union futex_key *key2,
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struct futex_pi_state **ps)
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struct futex_pi_state **ps, int set_waiters)
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{
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struct futex_q *top_waiter;
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struct futex_q *top_waiter = NULL;
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u32 curval;
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int ret;
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if (get_futex_value_locked(&curval, pifutex))
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return -EFAULT;
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/*
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* Find the top_waiter and determine if there are additional waiters.
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* If the caller intends to requeue more than 1 waiter to pifutex,
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* force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
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* as we have means to handle the possible fault. If not, don't set
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* the bit unecessarily as it will force the subsequent unlock to enter
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* the kernel.
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*/
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top_waiter = futex_top_waiter(hb1, key1);
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/* There are no waiters, nothing for us to do. */
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@ -1038,10 +1054,12 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
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return 0;
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/*
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* Either take the lock for top_waiter or set the FUTEX_WAITERS bit.
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* The pi_state is returned in ps in contended cases.
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* Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
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* the contended case or if set_waiters is 1. The pi_state is returned
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* in ps in contended cases.
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*/
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ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task);
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ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
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set_waiters);
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if (ret == 1)
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requeue_pi_wake_futex(top_waiter, key2);
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@ -1146,9 +1164,14 @@ retry_private:
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}
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if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
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/* Attempt to acquire uaddr2 and wake the top_waiter. */
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/*
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* Attempt to acquire uaddr2 and wake the top waiter. If we
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* intend to requeue waiters, force setting the FUTEX_WAITERS
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* bit. We force this here where we are able to easily handle
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* faults rather in the requeue loop below.
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*/
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ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
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&key2, &pi_state);
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&key2, &pi_state, nr_requeue);
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/*
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* At this point the top_waiter has either taken uaddr2 or is
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@ -1810,7 +1833,7 @@ retry:
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retry_private:
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hb = queue_lock(&q);
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ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current);
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ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
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if (unlikely(ret)) {
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switch (ret) {
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case 1:
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