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Merge branch 'core-futexes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 

* 'core-futexes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  futex: Detect mismatched requeue targets
  futex: Correct futex_wait_requeue_pi() commentary
This commit is contained in:
Linus Torvalds 2009-09-11 13:16:22 -07:00
parent 989aa44a5f 84bc4af590
commit 7193bea53f
1 changed files with 30 additions and 17 deletions
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47
kernel/futex.c
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@ -115,6 +115,9 @@ struct futex_q {
/* rt_waiter storage for requeue_pi: */
struct rt_mutex_waiter *rt_waiter;
/* The expected requeue pi target futex key: */
union futex_key *requeue_pi_key;
/* Bitset for the optional bitmasked wakeup */
u32 bitset;
};
@ -1089,6 +1092,10 @@ static int futex_proxy_trylock_atomic(u32 __user *pifutex,
if (!top_waiter)
return 0;
/* Ensure we requeue to the expected futex. */
if (!match_futex(top_waiter->requeue_pi_key, key2))
return -EINVAL;
/*
* 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
@ -1276,6 +1283,12 @@ retry_private:
continue;
}
/* Ensure we requeue to the expected futex for requeue_pi. */
if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
ret = -EINVAL;
break;
}
/*
* Requeue nr_requeue waiters and possibly one more in the case
* of requeue_pi if we couldn't acquire the lock atomically.
@ -1751,6 +1764,7 @@ static int futex_wait(u32 __user *uaddr, int fshared,
q.pi_state = NULL;
q.bitset = bitset;
q.rt_waiter = NULL;
q.requeue_pi_key = NULL;
if (abs_time) {
to = &timeout;
@ -1858,6 +1872,7 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
q.pi_state = NULL;
q.rt_waiter = NULL;
q.requeue_pi_key = NULL;
retry:
q.key = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE);
@ -2118,11 +2133,11 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
* We call schedule in futex_wait_queue_me() when we enqueue and return there
* via the following:
* 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
* 2) wakeup on uaddr2 after a requeue and subsequent unlock
* 3) signal (before or after requeue)
* 4) timeout (before or after requeue)
* 2) wakeup on uaddr2 after a requeue
* 3) signal
* 4) timeout
*
* If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.
* If 3, cleanup and return -ERESTARTNOINTR.
*
* If 2, we may then block on trying to take the rt_mutex and return via:
* 5) successful lock
@ -2130,7 +2145,7 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
* 7) timeout
* 8) other lock acquisition failure
*
* If 6, we setup a restart_block with futex_lock_pi() as the function.
* If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
*
* If 4 or 7, we cleanup and return with -ETIMEDOUT.
*
@ -2169,15 +2184,16 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
debug_rt_mutex_init_waiter(&rt_waiter);
rt_waiter.task = NULL;
q.pi_state = NULL;
q.bitset = bitset;
q.rt_waiter = &rt_waiter;
key2 = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out;
q.pi_state = NULL;
q.bitset = bitset;
q.rt_waiter = &rt_waiter;
q.requeue_pi_key = &key2;
/* Prepare to wait on uaddr. */
ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
if (ret)
@ -2248,14 +2264,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
rt_mutex_unlock(pi_mutex);
} else if (ret == -EINTR) {
/*
* We've already been requeued, but we have no way to
* restart by calling futex_lock_pi() directly. We
* could restart the syscall, but that will look at
* the user space value and return right away. So we
* drop back with EWOULDBLOCK to tell user space that
* "val" has been changed. That's the same what the
* restart of the syscall would do in
* futex_wait_setup().
* We've already been requeued, but cannot restart by calling
* futex_lock_pi() directly. We could restart this syscall, but
* it would detect that the user space "val" changed and return
* -EWOULDBLOCK. Save the overhead of the restart and return
* -EWOULDBLOCK directly.
*/
ret = -EWOULDBLOCK;
}