Re: [Patch] shm bug introduced with pagecache in 2.3.11

Manfred Spraul (manfreds@colorfullife.com)
Sat, 20 Nov 1999 16:28:14 +0100

Alan Cox wrote:
>
> > /* 3 asm instructions */
> > void release_exclusive(struct rw_mutex* rwm)
> > {
> > read_unlock(&rwm->rwl);
> > if(rwm->wake_me_up) {
> > rwm->wake_me_up = 0;
> > wake_up(&rwm->wait);
> > }
> > }
>
> That can race with another acquire surely. Suppose they set rmw->wake_me_up
> and we then continue our release and clear it.

But then we call wake_up(), we wake-up the second thread.
Now the second thread either acquires the lock, or it sets the value
back to 1.
This should be OK.

> Actually why do you want the wake_me_up field ?

I thought that would simplify the code. But unfortunately,
write_lock_trylock() is not atomic, and this means my proposal is
impossible.

I'm searching for another solution.

--
	Manfred


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/