Re: [PATCH 1/3] futex: do not pagefault_disable in futex_atomic_cmpxchg_inatomic()

[Linus Torvalds]

On Thu, Mar 10, 2011 at 6:47 PM, Michel Lespinasse <walken@xxxxxxxxxx> wrote:
> kernel/futex.c disables page faults before calling
> futex_atomic_cmpxchg_inatomic(), so there is no need to do it again
> within that function.

This seems totally bogus.

Even the comment is crap.

Sure, the callers may disable preemption, but that has NOTHING to do
with "pagefault_disable()". Th epagefault_[en/dis]able functions will
touch the preempt count EVEN IF PREEMPTION ISN'T EVEN ENABLED!

So what the f*ck does that "Note that preemption is disabled.." crap even mean?

The thing is made even worse by the fact that as far as I can tell,
the comment simply isn't true at all (even if you were to ignore the
fundamental confusion about preemption vs the pagefault
disable/enable). Not all callers of futex_atomic_cmpxchg_inatomic() do
anything of the sort, whether it's preemptibility _or_ the proper
pagefault_disable/enable(). Just look at the exit_robust_list() ->
handle_futex_death(), for example.

This kind of patch is the kind that personally makes me want to put
you on a spam-list. Misleading commit messages with bogus and
fundamentally incorrect added comments in the code. WTF?

Did I miss some patch that changed that, or is this really as horribly
bad as I think it is? I see it already made it into -tip.

                              Linus
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