On Mon, Feb 15, 2021 at 12:23:52PM -0300, André Almeida wrote:
> +static int futex_dequeue_multiple(struct futexv_head *futexv, unsigned int nr)
> +{
> + int i, ret = -1;
> +
> + for (i = 0; i < nr; i++) {
> + spin_lock(&futexv->objects[i].bucket->lock);
> + if (!list_empty_careful(&futexv->objects[i].list)) {
> + list_del_init_careful(&futexv->objects[i].list);
> + bucket_dec_waiters(futexv->objects[i].bucket);
What's with the careful? AFAICT all sites have that bucket->lock.
> + } else {
> + ret = i;
> + }
> + spin_unlock(&futexv->objects[i].bucket->lock);
> + }
> +
> + return ret;
> +}
> +static int futex_enqueue(struct futexv_head *futexv, unsigned int nr_futexes,
> + int *awakened)
> +{
> + int i, ret;
> + u32 uval, *uaddr, val;
> + struct futex_bucket *bucket;
> +
> +retry:
> + set_current_state(TASK_INTERRUPTIBLE);
> +
> + for (i = 0; i < nr_futexes; i++) {
> + uaddr = (u32 * __user)futexv->objects[i].uaddr;
> + val = (u32)futexv->objects[i].val;
> +
> + bucket = futexv->objects[i].bucket;
> +
> + bucket_inc_waiters(bucket);
> + spin_lock(&bucket->lock);
> +
> + ret = futex_get_user(&uval, uaddr);
> +
> + if (unlikely(ret)) {
> + spin_unlock(&bucket->lock);
> +
> + bucket_dec_waiters(bucket);
> + __set_current_state(TASK_RUNNING);
> + *awakened = futex_dequeue_multiple(futexv, i);
> +
> + if (__get_user(uval, uaddr))
> + return -EFAULT;
> +
> + if (*awakened >= 0)
> + return 1;
> +
> + goto retry;
> + }
> +
> + if (uval != val) {
> + spin_unlock(&bucket->lock);
> +
> + bucket_dec_waiters(bucket);
> + __set_current_state(TASK_RUNNING);
> + *awakened = futex_dequeue_multiple(futexv, i);
> +
> + if (*awakened >= 0)
> + return 1;
> +
> + return -EAGAIN;
> + }
> +
> + list_add_tail(&futexv->objects[i].list, &bucket->list);
and here
> + spin_unlock(&bucket->lock);
> + }
> +
> + return 0;
> +}
> +
> +static void futex_mark_wake(struct futex_waiter *waiter,
> + struct futex_bucket *bucket,
> + struct wake_q_head *wake_q)
> +{
> + struct task_struct *task;
> + struct futexv_head *parent = futex_get_parent((uintptr_t)waiter,
> + waiter->index);
> +
lockdep_assert_held(&bucket->lock);
> + parent->hint = true;
> + task = parent->task;
> + get_task_struct(task);
> + list_del_init_careful(&waiter->list);
and here
> + wake_q_add_safe(wake_q, task);
> + bucket_dec_waiters(bucket);
> +}
