Re: [PATCH -v4 5/7] locking, arch: Update spin_unlock_wait()

From: Peter Zijlstra
Date: Thu Jun 02 2016 - 10:45:09 EST

On Thu, Jun 02, 2016 at 10:24:40PM +0800, Boqun Feng wrote:
> On Thu, Jun 02, 2016 at 01:52:02PM +0200, Peter Zijlstra wrote:
> About spin_unlock_wait() on ppc, I actually have a fix pending review:

Please use the normal commit quoting style:

d86b8da04dfa ("arm64: spinlock: serialise spin_unlock_wait against concurrent lockers")

> that patch fixed a different problem when people want to pair a
> spin_unlock_wait() with a spin_lock().

Argh, indeed, and I think qspinlock is still broken there :/ But my poor
brain is about to give in for the day.

Let me go ponder that some :/

> I think we still need that fix, and there are two conflicts with this
> series:
> 1. arch_spin_unlock_wait() code for PPC32 was deleted, and
> consolidated into one.


> 2. I actually downgraded spin_unlock_wait() to !ACQUIRE ;-)

Fail ;-)

> I can think of two ways to solve thoes conflicts:
> 1. Modify my patch to make spin_unlock_wait() an ACQUIRE, and it
> can be merged in powerpc tree, and possible go into to mainline
> before 4.7. Then there is no need for this series to have code
> for ppc, therefore no conflict.

Hardly any other unlock_wait is an acquire, everyone is 'broken' :-/

> or
> 2. I can rebase my patch on this series, and it can be added in
> this series, and will go into mainline at 4.8.
> Michael and Peter, any thought?

I'm fine with it going in early, I can rebase, no problem.