diff options
Diffstat (limited to 'kernel/futex.c')
| -rw-r--r-- | kernel/futex.c | 98 |
1 files changed, 55 insertions, 43 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index 30e7daebaec8..04164d440d98 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1454,8 +1454,23 @@ static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, newval |= FUTEX_WAITERS; ret = lock_pi_update_atomic(uaddr, uval, newval); - /* If the take over worked, return 1 */ - return ret < 0 ? ret : 1; + if (ret) + return ret; + + /* + * If the waiter bit was requested the caller also needs PI + * state attached to the new owner of the user space futex. + * + * @task is guaranteed to be alive and it cannot be exiting + * because it is either sleeping or waiting in + * futex_requeue_pi_wakeup_sync(). + */ + if (set_waiters) { + ret = attach_to_pi_owner(uaddr, newval, key, ps, + exiting); + WARN_ON(ret); + } + return 1; } /* @@ -2036,17 +2051,24 @@ futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1, return -EAGAIN; /* - * 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 - * in ps in contended cases. + * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit + * in the contended case or if @set_waiters is true. + * + * In the contended case PI state is attached to the lock owner. If + * the user space lock can be acquired then PI state is attached to + * the new owner (@top_waiter->task) when @set_waiters is true. */ vpid = task_pid_vnr(top_waiter->task); ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, exiting, set_waiters); if (ret == 1) { - /* Dequeue, wake up and update top_waiter::requeue_state */ + /* + * Lock was acquired in user space and PI state was + * attached to @top_waiter->task. That means state is fully + * consistent and the waiter can return to user space + * immediately after the wakeup. + */ requeue_pi_wake_futex(top_waiter, key2, hb2); - return vpid; } else if (ret < 0) { /* Rewind top_waiter::requeue_state */ futex_requeue_pi_complete(top_waiter, ret); @@ -2208,19 +2230,26 @@ retry_private: &exiting, nr_requeue); /* - * At this point the top_waiter has either taken uaddr2 or is - * waiting on it. If the former, then the pi_state will not - * exist yet, look it up one more time to ensure we have a - * reference to it. If the lock was taken, @ret contains the - * VPID of the top waiter task. - * If the lock was not taken, we have pi_state and an initial - * refcount on it. In case of an error we have nothing. + * At this point the top_waiter has either taken uaddr2 or + * is waiting on it. In both cases pi_state has been + * established and an initial refcount on it. In case of an + * error there's nothing. * * The top waiter's requeue_state is up to date: * - * - If the lock was acquired atomically (ret > 0), then + * - If the lock was acquired atomically (ret == 1), then * the state is Q_REQUEUE_PI_LOCKED. * + * The top waiter has been dequeued and woken up and can + * return to user space immediately. The kernel/user + * space state is consistent. In case that there must be + * more waiters requeued the WAITERS bit in the user + * space futex is set so the top waiter task has to go + * into the syscall slowpath to unlock the futex. This + * will block until this requeue operation has been + * completed and the hash bucket locks have been + * dropped. + * * - If the trylock failed with an error (ret < 0) then * the state is either Q_REQUEUE_PI_NONE, i.e. "nothing * happened", or Q_REQUEUE_PI_IGNORE when there was an @@ -2234,36 +2263,20 @@ retry_private: * the same sanity checks for requeue_pi as the loop * below does. */ - if (ret > 0) { - WARN_ON(pi_state); - task_count++; - /* - * If futex_proxy_trylock_atomic() acquired the - * user space futex, then the user space value - * @uaddr2 has been set to the @hb1's top waiter - * task VPID. This task is guaranteed to be alive - * and cannot be exiting because it is either - * sleeping or blocked on @hb2 lock. - * - * The @uaddr2 futex cannot have waiters either as - * otherwise futex_proxy_trylock_atomic() would not - * have succeeded. - * - * In order to requeue waiters to @hb2, pi state is - * required. Hand in the VPID value (@ret) and - * allocate PI state with an initial refcount on - * it. - */ - ret = attach_to_pi_owner(uaddr2, ret, &key2, &pi_state, - &exiting); - WARN_ON(ret); - } - switch (ret) { case 0: /* We hold a reference on the pi state. */ break; + case 1: + /* + * futex_proxy_trylock_atomic() acquired the user space + * futex. Adjust task_count. + */ + task_count++; + ret = 0; + break; + /* * If the above failed, then pi_state is NULL and * waiter::requeue_state is correct. @@ -2395,9 +2408,8 @@ retry_private: } /* - * We took an extra initial reference to the pi_state either in - * futex_proxy_trylock_atomic() or in attach_to_pi_owner(). We need - * to drop it here again. + * We took an extra initial reference to the pi_state in + * futex_proxy_trylock_atomic(). We need to drop it here again. */ put_pi_state(pi_state); |