Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation

[Nikita Danilov <nikita@clusterfs.com>]

Andrew Morton writes:
 > Mark Lord <lkml@rtr.ca> wrote:
 > >
 > > Leaving up()/down() as-is is really the most sensible option.
 > >
 > 
 > Absolutely.
 > 
 > I must say that my interest in this stuff is down in
 > needs-an-electron-microscope-to-locate territory.  down() and up() work
 > just fine and they're small, efficient, well-debugged and well-understood. 
 > We need a damn good reason for taking on tree-wide churn or incompatible
 > renames or addition of risk.  What's the damn good reason here?
 > 
 > Please.  Go fix some bugs.  We're not short of them.

But this change is about fixing bugs: mutex assumes that

 - only owner can unlock, and

 - owner cannot lock (immediate self-deadlock).

This can be checked by the debugging code, and yes, these kinds of
errors do happen.

Not to say that by looking at

        struct foo_bar_baz {
                struct mutex fbb_mutex;
                ...
        };

one can instantly infer that ->fbb_mutex is used to serialize something
rather than serves as some fancy signaling mechanism.

Nikita.
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