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    SubjectRe: Linux 3.1-rc9
    On Thu, Oct 13, 2011 at 4:25 PM, Simon Kirby <sim@hostway.ca> wrote:
    >
    > Looks good. No hangs or crashes for two days on any of them running
    > 3.1-rc9 plus this patch. Not sure if you want to deuglify it, but it
    > seems to work...
    >
    > Tested-by: Simon Kirby <sim@hostway.ca>

    Peter, what's the status of this one?

    Quite frankly, I personally consider it to be broken - why are we
    introducing this new lock for this very special thing? A spinlock to
    protect a *single* word of counter seems broken.

    It seems more likely that the real bug is that kernel/sched_stats.h
    currently takes cputimer->lock without disabling interrupts. Everybody
    else uses irq-safe locking, why would sched_stats.h not need that?

    However, I don't see why that spinlock is needed at all. Why aren't
    those fields just atomics (or at least just "sum_exec_runtime")? And
    why does "cputime_add()" exist at all? It seems to always be just a
    plain add, and nothing else would seem to ever make sense *anyway*?

    In other words, none of that code makes any sense to me at all. And
    the patch in question that fixes a hang for Simon seems to make it
    even worse. Can somebody explain to me why it looks that crappy?

    Please?

    That stupid definition of cputime_add() has apparently existed as-is
    since it was introduced in 2005. Why do we have code like this:

    times->utime = cputime_add(times->utime, t->utime);

    instead of just

    times->utime += t->utime;

    which seems not just shorter, but more readable too? The reason is not
    some type safety in the cputime_add() thing, it's just a macro.

    Added Martin and Ingo to the discussion - Martin because he added that
    cputime_add in the first place, and Ingo because he gets the most hits
    on kernel/sched_stats.h. Guys - you can see the history on lkml.

    Linus


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