Re: pserialize(9) vs. TAILQ

[Masao Uebayashi <uebayasi%gmail.com@localhost>]

On Tue, Nov 25, 2014 at 1:44 AM, Eduardo Horvath <eeh%netbsd.org@localhost> wrote:
> Yes, the existing code assumes TSO.  A while back I was looking in to fixing that.
>
> I enhanced membar_ops with proper memory barriers and then was looking at
> the mutex code.  Unfortunately, I didn't get very far.  It seemed at the
> time that the mutex code has two hooks for memory barriers after the
> atomic operations, however it's missing memory barrier hooks to ensure
> consistency before accessing the lock.

My understanding is that checking mtx_owner, which is usually
"volatile uintptr_t mtxa_owner", doesn't need memory barrier, assuming
"volatile" works as expected (always read from memory).