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futex: split out fixup owner logic from futex_lock_pi()
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Refactor the post lock acquisition logic from futex_lock_pi(). This
code will be reused in futex_wait_requeue_pi().

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Darren Hart authored and Thomas Gleixner committed Apr 6, 2009
1 parent 1a52084 commit dd97399
Showing 1 changed file with 89 additions and 69 deletions.
158 changes: 89 additions & 69 deletions kernel/futex.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1255,6 +1255,79 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,

static long futex_wait_restart(struct restart_block *restart);

/**
* fixup_owner() - Post lock pi_state and corner case management
* @uaddr: user address of the futex
* @fshared: whether the futex is shared (1) or not (0)
* @q: futex_q (contains pi_state and access to the rt_mutex)
* @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
*
* After attempting to lock an rt_mutex, this function is called to cleanup
* the pi_state owner as well as handle race conditions that may allow us to
* acquire the lock. Must be called with the hb lock held.
*
* Returns:
* 1 - success, lock taken
* 0 - success, lock not taken
* <0 - on error (-EFAULT)
*/
static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
int locked)
{
struct task_struct *owner;
int ret = 0;

if (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:
*/
if (q->pi_state->owner != current)
ret = fixup_pi_state_owner(uaddr, q, current, fshared);
goto out;
}

/*
* Catch the rare case, where the lock was released when we were on the
* way back before we locked the hash bucket.
*/
if (q->pi_state->owner == current) {
/*
* Try to get the rt_mutex now. This might fail as some other
* task acquired the rt_mutex after we removed ourself from the
* rt_mutex waiters list.
*/
if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
locked = 1;
goto out;
}

/*
* pi_state is incorrect, some other task did a lock steal and
* we returned due to timeout or signal without taking the
* rt_mutex. Too late. We can access the rt_mutex_owner without
* locking, as the other task is now blocked on the hash bucket
* lock. Fix the state up.
*/
owner = rt_mutex_owner(&q->pi_state->pi_mutex);
ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
goto out;
}

/*
* Paranoia check. If we did not take the lock, then we should not be
* the owner, nor the pending owner, of the rt_mutex.
*/
if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
"pi-state %p\n", ret,
q->pi_state->pi_mutex.owner,
q->pi_state->owner);

out:
return ret ? ret : locked;
}

/**
* futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
* @hb: the futex hash bucket, must be locked by the caller
Expand Down Expand Up @@ -1459,11 +1532,10 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
int detect, ktime_t *time, int trylock)
{
struct hrtimer_sleeper timeout, *to = NULL;
struct task_struct *curr = current;
struct futex_hash_bucket *hb;
u32 uval;
struct futex_q q;
int ret;
int res, ret;

if (refill_pi_state_cache())
return -ENOMEM;
Expand Down Expand Up @@ -1527,81 +1599,29 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
}

spin_lock(q.lock_ptr);

if (!ret) {
/*
* Got the lock. We might not be the anticipated owner
* if we did a lock-steal - fix up the PI-state in
* that case:
*/
if (q.pi_state->owner != curr)
ret = fixup_pi_state_owner(uaddr, &q, curr, fshared);
} else {
/*
* Catch the rare case, where the lock was released
* when we were on the way back before we locked the
* hash bucket.
*/
if (q.pi_state->owner == curr) {
/*
* Try to get the rt_mutex now. This might
* fail as some other task acquired the
* rt_mutex after we removed ourself from the
* rt_mutex waiters list.
*/
if (rt_mutex_trylock(&q.pi_state->pi_mutex))
ret = 0;
else {
/*
* pi_state is incorrect, some other
* task did a lock steal and we
* returned due to timeout or signal
* without taking the rt_mutex. Too
* late. We can access the
* rt_mutex_owner without locking, as
* the other task is now blocked on
* the hash bucket lock. Fix the state
* up.
*/
struct task_struct *owner;
int res;

owner = rt_mutex_owner(&q.pi_state->pi_mutex);
res = fixup_pi_state_owner(uaddr, &q, owner,
fshared);

/* propagate -EFAULT, if the fixup failed */
if (res)
ret = res;
}
} else {
/*
* Paranoia check. If we did not take the lock
* in the trylock above, then we should not be
* the owner of the rtmutex, neither the real
* nor the pending one:
*/
if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
printk(KERN_ERR "futex_lock_pi: ret = %d "
"pi-mutex: %p pi-state %p\n", ret,
q.pi_state->pi_mutex.owner,
q.pi_state->owner);
}
}
/*
* Fixup the pi_state owner and possibly acquire the lock if we
* haven't already.
*/
res = fixup_owner(uaddr, fshared, &q, !ret);
/*
* If fixup_owner() returned an error, proprogate that. If it acquired
* the lock, clear our -ETIMEDOUT or -EINTR.
*/
if (res)
ret = (res < 0) ? res : 0;

/*
* If fixup_pi_state_owner() faulted and was unable to handle the
* fault, unlock it and return the fault to userspace.
* If fixup_owner() faulted and was unable to handle the fault, unlock
* it and return the fault to userspace.
*/
if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
rt_mutex_unlock(&q.pi_state->pi_mutex);

/* Unqueue and drop the lock */
unqueue_me_pi(&q);

if (to)
destroy_hrtimer_on_stack(&to->timer);
return ret != -EINTR ? ret : -ERESTARTNOINTR;
goto out;

out_unlock_put_key:
queue_unlock(&q, hb);
Expand All @@ -1611,7 +1631,7 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
out:
if (to)
destroy_hrtimer_on_stack(&to->timer);
return ret;
return ret != -EINTR ? ret : -ERESTARTNOINTR;

uaddr_faulted:
/*
Expand Down

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