Re: a competition when some threads acquire futex

[chengjian (D)]

> > diff --git a/kernel/futex.c b/kernel/futex.c
> > index 3d38eaf..0b2d17a 100644
> > --- a/kernel/futex.c
> > +++ b/kernel/futex.c
> > @@ -1545,6 +1545,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval,
> > struct futex_pi_state *pi_
> >    	spin_unlock(&hb->lock);
> >   	wake_up_q(&wake_q);
> > +        _cond_resched( );

Hi Thomas,

I wrote _cond_resched( ) in futex_wake( ) which will be called to wake 
up waiters
when the process release the futex.


But the patch producted by git format-patch displayed in wake_futex_pi( ).


```c

/*
 * Wake up waiters matching bitset queued on this futex (uaddr).
 */
static int
futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
{
    struct futex_hash_bucket *hb;
    struct futex_q *this, *next;
    union futex_key key = FUTEX_KEY_INIT;
    int ret;
    DEFINE_WAKE_Q(wake_q);

    if (!bitset)
        return -EINVAL;

    ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
    if (unlikely(ret != 0))
        goto out;

    hb = hash_futex(&key);

    /* Make sure we really have tasks to wakeup */
    if (!hb_waiters_pending(hb))
        goto out_put_key;

    spin_lock(&hb->lock);

    plist_for_each_entry_safe(this, next, &hb->chain, list) {
        if (match_futex (&this->key, &key)) {
            if (this->pi_state || this->rt_waiter) {
                ret = -EINVAL;
                break;
            }

            /* Check if one of the bits is set in both bitsets */
            if (!(this->bitset & bitset))
                continue;

            mark_wake_futex(&wake_q, this);
            if (++ret >= nr_wake)
                break;
        }
    }

    spin_unlock(&hb->lock);
    wake_up_q(&wake_q);

+ _cond_resched( );
out_put_key:
    put_futex_key(&key);
out:
    return ret;
}
```



Thanks.

Cheng Jian