Re: [patch 4/8] futex: Add support for unlocking robust futexes

[Florian Weimer]

* Peter Zijlstra:

>> No. There is a syscall in between and if that is not sufficient then the
>> architecure has more severe troubles than that store, no?
>
> So I think we once tried to determine if syscall could be considered to
> imply memory ordering, and I think the take-away at the time was that we
> could not assume so.
>
> But its been a long time, maybe I misremember.

I remember the same thing, and I think I saw test failures where system
calls where not a (strong) barrier on POWER.

However, some system calls better be barriers.  For example, writing to
a pipe should synchronize with reading from the pipe and poll wakeup on
the read end.  Likewise for sockets, I assume.  As far as I know, POSIX
is silent on this topic, though.

Thanks,
Florian