linux-kernel - Re: [PATCH -v4 5/7] locking, arch: Update spin_unlock

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Message-ID: <20160602144424.GV3193@twins.programming.kicks-ass.net>
Date:	Thu, 2 Jun 2016 16:44:24 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Boqun Feng <boqun.feng@...il.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	manfred@...orfullife.com, dave@...olabs.net,
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Subject: Re: [PATCH -v4 5/7] locking, arch: Update spin_unlock_wait()

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:
> 
> http://lkml.kernel.org/r/1461130033-70898-1-git-send-email-boqun.feng@gmail.com

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.

Nice.

> 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.