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Message-ID: <CA+55aFyyHbPVMx8cZbKONy5cevxsYA0qbwapboA0dD8hPSwPWg@mail.gmail.com> Date: Tue, 24 May 2016 09:17:13 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Peter Zijlstra <peterz@...radead.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 7:27 AM, Peter Zijlstra <peterz@...radead.org> wrote: > spin_unlock_wait() has an unintuitive 'feature' in that it doesn't > fully serialize against the spin_unlock() we've waited on. NAK. We don't start adding more of this "after_ctrl_dep" crap. It's completely impossible to understand, and even people who have been locking experts have gotten it wrong. So it is *completely* unacceptable to have it in drivers. 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. The difference is that one talks about incomprehensible implementation details that nobody outside of the person who *implemented* the spinlock code is supposed to understand (and seriously, I have my doubts even the spinlock implementer understands it, judging by the last time this happened), and the other is a much simpler semantic guarantee. So don't talk about "acquire". And most certainly don't talk about "control dependencies". Not if we end up having things like *drivers* using this like in this example libata. Linus
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