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futex: fixup unlocked requeue pi case

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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>
This commit is contained in:
Darren Hart 2009-04-07 23:23:50 -07:00 committed by Thomas Gleixner
parent 52400ba946
commit bab5bc9e85
1 changed files with 44 additions and 21 deletions
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65
kernel/futex.c
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@ -565,12 +565,14 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
/**
* futex_lock_pi_atomic() - atomic work required to acquire a pi aware futex
* @uaddr: the pi futex user address
* @hb: the pi futex hash bucket
* @key: the futex key associated with uaddr and hb
* @ps: the pi_state pointer where we store the result of the lookup
* @task: the task to perform the atomic lock work for. This will be
* "current" except in the case of requeue pi.
* @uaddr: the pi futex user address
* @hb: the pi futex hash bucket
* @key: the futex key associated with uaddr and hb
* @ps: the pi_state pointer where we store the result of the
* lookup
* @task: the task to perform the atomic lock work for. This will
* be "current" except in the case of requeue pi.
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
*
* Returns:
* 0 - ready to wait
@ -582,7 +584,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
union futex_key *key,
struct futex_pi_state **ps,
struct task_struct *task)
struct task_struct *task, int set_waiters)
{
int lock_taken, ret, ownerdied = 0;
u32 uval, newval, curval;
@ -596,6 +598,8 @@ retry:
* the locks. It will most likely not succeed.
*/
newval = task_pid_vnr(task);
if (set_waiters)
newval |= FUTEX_WAITERS;
curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
@ -1004,14 +1008,18 @@ void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key)
/**
* futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
* @pifutex: the user address of the to futex
* @hb1: the from futex hash bucket, must be locked by the caller
* @hb2: the to futex hash bucket, must be locked by the caller
* @key1: the from futex key
* @key2: the to futex key
* @pifutex: the user address of the to futex
* @hb1: the from futex hash bucket, must be locked by the caller
* @hb2: the to futex hash bucket, must be locked by the caller
* @key1: the from futex key
* @key2: the to futex key
* @ps: address to store the pi_state pointer
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
*
* Try and get the lock on behalf of the top waiter if we can do it atomically.
* Wake the top waiter if we succeed. hb1 and hb2 must be held by the caller.
* Wake the top waiter if we succeed. If the caller specified set_waiters,
* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
* hb1 and hb2 must be held by the caller.
*
* Returns:
* 0 - failed to acquire the lock atomicly
@ -1022,15 +1030,23 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
struct futex_hash_bucket *hb1,
struct futex_hash_bucket *hb2,
union futex_key *key1, union futex_key *key2,
struct futex_pi_state **ps)
struct futex_pi_state **ps, int set_waiters)
{
struct futex_q *top_waiter;
struct futex_q *top_waiter = NULL;
u32 curval;
int ret;
if (get_futex_value_locked(&curval, pifutex))
return -EFAULT;
/*
* Find the top_waiter and determine if there are additional waiters.
* If the caller intends to requeue more than 1 waiter to pifutex,
* force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
* as we have means to handle the possible fault. If not, don't set
* the bit unecessarily as it will force the subsequent unlock to enter
* the kernel.
*/
top_waiter = futex_top_waiter(hb1, key1);
/* There are no waiters, nothing for us to do. */
@ -1038,10 +1054,12 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
return 0;
/*
* Either take the lock for top_waiter or set the FUTEX_WAITERS bit.
* The pi_state is returned in ps in contended cases.
* Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
* the contended case or if set_waiters is 1. The pi_state is returned
* in ps in contended cases.
*/
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task);
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
set_waiters);
if (ret == 1)
requeue_pi_wake_futex(top_waiter, key2);
@ -1146,9 +1164,14 @@ retry_private:
}
if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
/* Attempt to acquire uaddr2 and wake the top_waiter. */
/*
* Attempt to acquire uaddr2 and wake the top waiter. If we
* intend to requeue waiters, force setting the FUTEX_WAITERS
* bit. We force this here where we are able to easily handle
* faults rather in the requeue loop below.
*/
ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
&key2, &pi_state);
&key2, &pi_state, nr_requeue);
/*
* At this point the top_waiter has either taken uaddr2 or is
@ -1810,7 +1833,7 @@ retry:
retry_private:
hb = queue_lock(&q);
ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current);
ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
if (unlikely(ret)) {
switch (ret) {
case 1: