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    SubjectRe: PREEMPT_ACTIVE too low error with all asm-generic headers for some arches
    On Wed, Jun 24, 2009 at 10:02, Arnd Bergmann wrote:
    > On Wednesday 24 June 2009, Ingo Molnar wrote:
    >> * Mike Frysinger <vapier.adi@gmail.com> wrote:
    >> > if we look at linux/hardirq.h, it makes this claim:
    >> >  * - bit 28 is the PREEMPT_ACTIVE flag
    >> > if that's true, then why are we letting any arch set this define ?  a
    >> > quick survey shows that half the arches (11) are using 0x10000000 (bit
    >> > 28) while the other half (10) are using 0x4000000 (bit 26).  and then
    >> > there is the ia64 oddity which uses bit 30.  the exact value here
    >> > shouldnt really matter across arches though should it ?
    >
    > actually alpha, arm and avr32 also use bit 30 (0x40000000), there are only
    > five (or eight, depending on how you count) architectures (blackfin, h8300,
    > m68k, s390 and sparc) using bit 26.

    meh, too many zeros ;)

    >> Correct - what matters is to have no collision between the fields.
    >>
    >> > how about adding this to linux/thread_info.h:
    >> > #ifndef PREEMPT_ACTIVE
    >> > # ifndef PREEMPT_ACTIVE_BIT
    >> > #  define PREEMPT_ACTIVE_BIT 28
    >> > # endif
    >> > # define PREEMPT_ACTIVE (1 << PREEMPT_ACTIVE_BIT)
    >> > #endif
    >>
    >> Makes sense i guess - but do we really need that level of
    >> #ifdef nesting? PREEMPT_ACTIVE_BIT should be the main control - with
    >> a default to 28 if it's not set. PREEMPT_ACTIVE is then derived off
    >> that, without any #ifdefs.
    >
    > I think it would fit better into linux/hardirq.h instead of
    > linux/thread_info.h, because that is where the other bits of
    > the preempt count are defined.

    agreed

    > --- a/include/linux/hardirq.h
    > +++ b/include/linux/hardirq.h
    > @@ -62,6 +62,12 @@
    >  #define HARDIRQ_OFFSET (1UL << HARDIRQ_SHIFT)
    >  #define NMI_OFFSET     (1UL << NMI_SHIFT)
    >
    > +#ifndef PREEMPT_ACTIVE
    > +#define PREEMPT_ACTIVE_BITS    1
    > +#define PREEMPT_ACTIVE_SHIFT   (NMI_SHIFT + NMI_BITS)
    > +#define PREEMPT_ACTIVE (__IRQ_MASK(PREEMPT_ACTIVE_BITS) << PREEMPT_SHIFT)

    i think you meant "<< PREEMPT_ACTIVE_SHIFT" there. once i make that
    change, it builds fine.
    -mike
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