[Linaro-mm-sig] [PATCH v3 2/3] mutex: add support for wound/wait style locks, v3

[Daniel Vetter]

On Thu, May 23, 2013 at 11:13 AM, Maarten Lankhorst
<maarten.lankhorst at canonical.com> wrote:
>> 2. Do you really want to drop the *_slow variants?
>> Doing so might reduce debugging slightly. I like method #2 in ww-mutex-design.txt, it makes it very clear why you
>> would handle the *_slow case differently anyway.
> As you pointed out, we wouldn't lose much debugging information.
> The same checks could be done in the normal variant with
> WARN_ON(ctx->lock && ctx->lock != lock);
> WARN_ON(ctx->lock && ctx->acquired > 0);

s/lock/contending_lock/ I guess. But yeah, I should have more
carefully read Peter's suggestion to fold in some of the ww_slow debug
checks, we can indeed keep the important debug checks even when
dropping slow. Silly me should be less sloppy.

> But it boils down to ww_mutex_lock_slow returning void instead of int __must_check from ww_mutex_lock.
>
> Maybe add inlines for *_slow, that use the ww_mutex_lock functions, and check ctx->lock == lock in debugging mode?

So either we keep the _slow versions or drop the __must_check for
ww_mutex_lock. In both cases the ww mutex user needs to think a bit
what to do, and I don't there's much we can do in the implementation
(beside all the existing debug support we have) to help. So now I'm
leaning more towards dropping the _slow variants to avoid interface
proliferation.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch