}
}
+enum futex_access {
+ FUTEX_READ,
+ FUTEX_WRITE
+};
+
/**
* get_futex_key() - Get parameters which are the keys for a futex
* @uaddr: virtual address of the futex
* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
* @key: address where result is stored.
- * @rw: mapping needs to be read/write (values: VERIFY_READ,
- * VERIFY_WRITE)
+ * @rw: mapping needs to be read/write (values: FUTEX_READ,
+ * FUTEX_WRITE)
*
* Return: a negative error code or 0
*
* lock_page() might sleep, the caller should not hold a spinlock.
*/
static int
-get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
+get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, enum futex_access rw)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
return -EINVAL;
address -= key->both.offset;
- if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
+ if (unlikely(!access_ok(uaddr, sizeof(u32))))
return -EFAULT;
if (unlikely(should_fail_futex(fshared)))
* If write access is not required (eg. FUTEX_WAIT), try
* and get read-only access.
*/
- if (err == -EFAULT && rw == VERIFY_READ) {
+ if (err == -EFAULT && rw == FUTEX_READ) {
err = get_user_pages_fast(address, 1, 0, &page);
ro = 1;
}
if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
return;
- /*
- * Queue the task for later wakeup for after we've released
- * the hb->lock. wake_q_add() grabs reference to p.
- */
- wake_q_add(wake_q, p);
+ get_task_struct(p);
__unqueue_futex(q);
/*
* The waiting task can free the futex_q as soon as q->lock_ptr = NULL
* plist_del in __unqueue_futex().
*/
smp_store_release(&q->lock_ptr, NULL);
+
+ /*
+ * Queue the task for later wakeup for after we've released
+ * the hb->lock. wake_q_add() grabs reference to p.
+ */
+ wake_q_add(wake_q, p);
+ put_task_struct(p);
}
/*
if (!bitset)
return -EINVAL;
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
if (unlikely(ret != 0))
goto out;
oparg = 1 << oparg;
}
- if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
+ if (!access_ok(uaddr, sizeof(u32)))
return -EFAULT;
ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
DEFINE_WAKE_Q(wake_q);
retry:
- ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
+ ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
if (unlikely(ret != 0))
goto out;
- ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
+ ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
if (unlikely(ret != 0))
goto out_put_key1;
}
retry:
- ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
+ ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
if (unlikely(ret != 0))
goto out;
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
- requeue_pi ? VERIFY_WRITE : VERIFY_READ);
+ requeue_pi ? FUTEX_WRITE : FUTEX_READ);
if (unlikely(ret != 0))
goto out_put_key1;
* decrement the counter at queue_unlock() when some error has
* occurred and we don't end up adding the task to the list.
*/
- hb_waiters_inc(hb);
+ hb_waiters_inc(hb); /* implies smp_mb(); (A) */
q->lock_ptr = &hb->lock;
- spin_lock(&hb->lock); /* implies smp_mb(); (A) */
+ spin_lock(&hb->lock);
return hb;
}
* while the syscall executes.
*/
retry:
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
if (unlikely(ret != 0))
return ret;
}
retry:
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
if (unlikely(ret != 0))
goto out;
* and BUG when futex_unlock_pi() interleaves with this.
*
* Therefore acquire wait_lock while holding hb->lock, but drop the
- * latter before calling rt_mutex_start_proxy_lock(). This still fully
- * serializes against futex_unlock_pi() as that does the exact same
- * lock handoff sequence.
+ * latter before calling __rt_mutex_start_proxy_lock(). This
+ * interleaves with futex_unlock_pi() -- which does a similar lock
+ * handoff -- such that the latter can observe the futex_q::pi_state
+ * before __rt_mutex_start_proxy_lock() is done.
*/
raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
spin_unlock(q.lock_ptr);
+ /*
+ * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
+ * such that futex_unlock_pi() is guaranteed to observe the waiter when
+ * it sees the futex_q::pi_state.
+ */
ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
if (ret) {
if (ret == 1)
ret = 0;
-
- spin_lock(q.lock_ptr);
- goto no_block;
+ goto cleanup;
}
-
if (unlikely(to))
hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
+cleanup:
spin_lock(q.lock_ptr);
/*
- * If we failed to acquire the lock (signal/timeout), we must
+ * If we failed to acquire the lock (deadlock/signal/timeout), we must
* first acquire the hb->lock before removing the lock from the
- * rt_mutex waitqueue, such that we can keep the hb and rt_mutex
- * wait lists consistent.
+ * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
+ * lists consistent.
*
* In particular; it is important that futex_unlock_pi() can not
* observe this inconsistency.
if ((uval & FUTEX_TID_MASK) != vpid)
return -EPERM;
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
if (ret)
return ret;
* there is no point where we hold neither; and therefore
* wake_futex_pi() must observe a state consistent with what we
* observed.
+ *
+ * In particular; this forces __rt_mutex_start_proxy() to
+ * complete such that we're guaranteed to observe the
+ * rt_waiter. Also see the WARN in wake_futex_pi().
*/
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);
*/
rt_mutex_init_waiter(&rt_waiter);
- ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
+ ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
if (unlikely(ret != 0))
goto out;
projects / linux-2.6-block.git / blobdiff