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futex: split out futex value validation code

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Refactor the code to validate the expected futex value in order to
reuse it with the requeue_pi code.

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Darren Hart 2009-04-03 13:40:40 -07:00 committed by Thomas Gleixner
parent 9121e4783c
commit f801073f87
1 changed files with 79 additions and 51 deletions
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130
kernel/futex.c
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@ -1398,6 +1398,82 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
__set_current_state(TASK_RUNNING);
}
/**
* futex_wait_setup() - Prepare to wait on a futex
* @uaddr: the futex userspace address
* @val: the expected value
* @fshared: whether the futex is shared (1) or not (0)
* @q: the associated futex_q
* @hb: storage for hash_bucket pointer to be returned to caller
*
* Setup the futex_q and locate the hash_bucket. Get the futex value and
* compare it with the expected value. Handle atomic faults internally.
* Return with the hb lock held and a q.key reference on success, and unlocked
* with no q.key reference on failure.
*
* Returns:
* 0 - uaddr contains val and hb has been locked
* <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
*/
static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
struct futex_q *q, struct futex_hash_bucket **hb)
{
u32 uval;
int ret;
/*
* Access the page AFTER the hash-bucket is locked.
* Order is important:
*
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
*
* The basic logical guarantee of a futex is that it blocks ONLY
* if cond(var) is known to be true at the time of blocking, for
* any cond. If we queued after testing *uaddr, that would open
* a race condition where we could block indefinitely with
* cond(var) false, which would violate the guarantee.
*
* A consequence is that futex_wait() can return zero and absorb
* a wakeup when *uaddr != val on entry to the syscall. This is
* rare, but normal.
*/
retry:
q->key = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr, fshared, &q->key);
if (unlikely(ret != 0))
goto out;
retry_private:
*hb = queue_lock(q);
ret = get_futex_value_locked(&uval, uaddr);
if (ret) {
queue_unlock(q, *hb);
ret = get_user(uval, uaddr);
if (ret)
goto out;
if (!fshared)
goto retry_private;
put_futex_key(fshared, &q->key);
goto retry;
}
if (uval != val) {
queue_unlock(q, *hb);
ret = -EWOULDBLOCK;
}
out:
if (ret)
put_futex_key(fshared, &q->key);
return ret;
}
static int futex_wait(u32 __user *uaddr, int fshared,
u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
{
@ -1406,7 +1482,6 @@ static int futex_wait(u32 __user *uaddr, int fshared,
struct restart_block *restart;
struct futex_hash_bucket *hb;
struct futex_q q;
u32 uval;
int ret;
if (!bitset)
@ -1425,57 +1500,10 @@ static int futex_wait(u32 __user *uaddr, int fshared,
current->timer_slack_ns);
}
retry:
q.key = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr, fshared, &q.key);
if (unlikely(ret != 0))
goto out;
retry_private:
hb = queue_lock(&q);
/*
* Access the page AFTER the hash-bucket is locked.
* Order is important:
*
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
*
* The basic logical guarantee of a futex is that it blocks ONLY
* if cond(var) is known to be true at the time of blocking, for
* any cond. If we queued after testing *uaddr, that would open
* a race condition where we could block indefinitely with
* cond(var) false, which would violate the guarantee.
*
* A consequence is that futex_wait() can return zero and absorb
* a wakeup when *uaddr != val on entry to the syscall. This is
* rare, but normal.
*
* For shared futexes, we hold the mmap semaphore, so the mapping
* cannot have changed since we looked it up in get_futex_key.
*/
ret = get_futex_value_locked(&uval, uaddr);
if (unlikely(ret)) {
queue_unlock(&q, hb);
ret = get_user(uval, uaddr);
/* Prepare to wait on uaddr. */
ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
if (ret)
goto out_put_key;
if (!fshared)
goto retry_private;
put_futex_key(fshared, &q.key);
goto retry;
}
ret = -EWOULDBLOCK;
/* Only actually queue if *uaddr contained val. */
if (unlikely(uval != val)) {
queue_unlock(&q, hb);
goto out_put_key;
}
goto out;
/* queue_me and wait for wakeup, timeout, or a signal. */
futex_wait_queue_me(hb, &q, to, &wait);