Messages in this thread | | | Date | Tue, 24 May 2016 09:17:13 -0700 | Subject | Re: [RFC][PATCH 2/3] locking: Annotate spin_unlock_wait() users | From | Linus Torvalds <> |
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On Tue, May 24, 2016 at 7:27 AM, Peter Zijlstra <peterz@infradead.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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