Subject: [-rt potential bug?] Bad error path in futex_wake
From: john stultz <johnstul@us.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>, Thomas Gleixner <tglx@linutronix.de>,
       lkml <linux-kernel@vger.kernel.org>,
       Dinakar Guniguntala <dino@in.ibm.com>
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Date: Mon, 15 May 2006 19:12:30 -0700
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Hey Ingo,
	I've been trying to help Dinakar chase down a futex bug where
lookup_pi_state oopses due to this->pi_state being NULL
(kernel/futex.c:480).

No clue on why yet, but looking over the code, I noticed the following
odd error path:

static int futex_wake(u32 __user *uaddr, int nr_wake)
{
        [snip]
	down_read(&current->mm->mmap_sem);

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

	hb = hash_futex(&key);
	spin_lock(&hb->lock);
	head = &hb->chain;

	list_for_each_entry_safe(this, next, head, list) {
		if (match_futex (&this->key, &key)) {
			if (this->pi_state)
!!!!------>			return -EINVAL;
			wake_futex(this);
			if (++ret >= nr_wake)
				break;
		}
	}

	spin_unlock(&hb->lock);
out:
	up_read(&current->mm->mmap_sem);
	return ret;
}

I'm not very familiar w/ the futex code, so this might be the right
thing, but it sure looks wrong.

Thoughts?

thanks
-john

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