Re: [RFC, PATCH 1/2] qrcu: "quick" srcu implementation

[Oleg Nesterov]

On 11/30, Oleg Nesterov wrote:
>
> On 11/29, Paul E. McKenney wrote:
> >
> > Hmmm...  Now I am wondering if the memory barriers inherent in the
> > __wait_event() suffice for this last barrier...  :-/  Thoughts?
> > 
> > > +	smp_mb();
> 
> Fastpath skips __wait_event(), and it is possible that the reader does
> lock/unlock between the first 'mb()' and 'if (atomic_read() == 1)'.

In fact, a slow path needs (I think) it too. We can have an unrelated
wakeup, and then the reader does unlock() before we check !atomic_read()
in the __wait_event()'s loop. The reader removes us from ->wq, in that
case finish_wait() does nothing.

Oleg.

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