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    SubjectRe: [ 57/72] genirq: Unmask oneshot irqs when thread was not woken
    On Tue, Mar 6, 2012 at 12:26 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
    >
    > Subject: genirq: Clear action->thread_mask if IRQ_ONESHOT is not set

    Umm. Apparently this patch fixes the bug, but the patch itself is just insane.

    > -       if (new->flags & IRQF_ONESHOT && thread_mask == ~0UL) {
    > -               ret = -EBUSY;
    > -               goto out_mask;
    > +       if (new->flags & IRQF_ONESHOT) {
    > +               if (thread_mask == ~0UL) {
    > +                       ret = -EBUSY;
    > +                       goto out_mask;
    > +               }
    > +               new->thread_mask = new->flags & IRQF_ONESHOT;
    >        }
    > -       new->thread_mask = 1 << ffz(thread_mask);

    WHAT?

    You just checked that "new->flags & IRQF_ONESHOT" nonzero, and inside
    that if-statement, you then do

    new->thread_mask = new->flags & IRQF_ONESHOT;

    which is just crazy. Why don't you just do

    new->thread_mask = IRQF_ONESHOT;

    if that is what you actually meant?

    What is that code actually *supposed* to do?

    Also, what was the meaning of that old insane line:

    new->thread_mask = 1 << ffz(thread_mask);

    which you removed? It was crap, I agree, but what was the thinking
    behind it? And the reason it was crap is because that's a crazy
    expression that could be written better ways (*), and it needs a
    comment on what the heck the point of it was..

    So stop with these "random code" snippets, and explain what the f*&^
    the code is meant to do, AND THEN WRITE THE CODE IN A SANE MANNER
    instead of posting these kinds of insane patches.

    Because right now it really looks like the "random monkey" approach to
    programming.

    Linus

    (*) "1 << ffz(a)" can be written as

    a = ~a; /* Turn the zero bits into 1 bits */
    a &= -a; /* .. and find the first one. */

    without ever doing any insane bit scanning.
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