Re: [PATCH] kvm: fix waitqueue_active without memory barrier in virt/kvm/async_pf.c

[Peter Zijlstra]

On Fri, Oct 09, 2015 at 10:45:32AM +0200, Paolo Bonzini wrote:
> So you need another smp_mb() after prepare_to_wait().  I'm not sure
> if it's needed also for your original tty report, but I think it is
> for https://lkml.org/lkml/2015/10/8/989 ("mei: fix waitqueue_active
> without memory barrier in mei drivers").
> 
> I wonder if it makes sense to introduce smp_mb__before_spin_lock()
> and smp_mb__after_spin_unlock().  On x86 the former could be a
> simple compiler barrier, and on s390 both of them could.  But that
> should be a separate patch.

Not having actually read or thought about the issue at hand, its
perfectly valid to pair an smp_mb() with either spin_lock() or
spin_unlock().

IOW. MB <-> {ACQUIRE, RELEASE} is a valid pairing.
--
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/