linux-kernel - Re: [RFC][PATCH 2/3] locking: Annotate spin_unlock

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Message-ID: <20160524165741.GB15189@worktop.bitpit.net>
Date:	Tue, 24 May 2016 18:57:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Will Deacon <will.deacon@....com>,
	Boqun Feng <boqun.feng@...il.com>,
	Waiman Long <Waiman.Long@....com>, Tejun Heo <tj@...nel.org>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Patrick McHardy <kaber@...sh.net>,
	David Miller <davem@...emloft.net>,
	Oleg Nesterov <oleg@...hat.com>,
	netfilter-devel@...r.kernel.org,
	Sasha Levin <sasha.levin@...cle.com>, hofrat@...dl.org
Subject: Re: [RFC][PATCH 2/3] locking: Annotate spin_unlock_wait() users

On Tue, May 24, 2016 at 09:17:13AM -0700, Linus Torvalds wrote:

> This needs to be either hidden inside the basic spinlock functions,
> _or_ it needs to be a clear and unambiguous interface. Anything that
> starts talking about control dependencies is not it.
> 
> Note that this really is about naming and use, not about
> implementation. So something like "spin_sync_after_unlock_wait()" is
> acceptable, even if the actual _implementation_ were to be exactly the
> same as the "after_ctrl_dep()" crap.

OK; so I would prefer to keep the smp_acquire__after_ctrl_dep() crap for
common use in smp_cond_acquire() and such, but I'd be more than happy to
just stuff it unconditionally into spin_unlock_wait().

Most users really need it, and its restores intuitive semantics to the
primitive.

I'm assuming the explicit use then left in ipc/sem.c (as paired with the
spin_is_locked) is fine with you; that's certainly not driver code.

Todays series was really more about auditing all the spin_unlock_wait()
usage sites.