From f801073f87aa22ddf0e9146355fec3993163790f Mon Sep 17 00:00:00 2001 From: Darren Hart Date: Fri, 3 Apr 2009 13:40:40 -0700 Subject: [PATCH] futex: split out futex value validation code Refactor the code to validate the expected futex value in order to reuse it with the requeue_pi code. Signed-off-by: Darren Hart Reviewed-by: Thomas Gleixner Signed-off-by: Thomas Gleixner --- kernel/futex.c | 130 ++++++++++++++++++++++++++++++------------------- 1 file changed, 79 insertions(+), 51 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index e76942e2a79f..dbe857aa4381 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -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) @@ -1425,58 +1500,11 @@ 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)) + /* Prepare to wait on uaddr. */ + ret = futex_wait_setup(uaddr, val, fshared, &q, &hb); + if (ret) 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); - 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; - } - /* queue_me and wait for wakeup, timeout, or a signal. */ futex_wait_queue_me(hb, &q, to, &wait);