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    SubjectRe: AGP bogosities
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    Linus Torvalds <torvalds@osdl.org> writes:

    > Hmm.. We seem to not have any tests for the counts becoming negative, and
    > this would seem to be an easy mistake to make considering that both I and
    > Dave did it.

    I stole this from -mm.
    --
    OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>


    From: Ingo Molnar <mingo@elte.hu>

    The patch below will detect atomic counter underflows. This has been
    test-driven in the -RT patchset for some time. qdisc_destroy() triggered
    it sometimes (in a seemingly nonfatal way, during device shutdown) - with
    DaveM suggesting that it is most likely a bug in the networking code. So
    it would be nice to have this in -mm for some time to validate all atomic
    counters on a broader base.

    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    Signed-off-by: Andrew Morton <akpm@osdl.org>
    ---

    25-akpm/include/asm-i386/atomic.h | 4 ++++
    1 files changed, 4 insertions(+)

    diff -puN include/asm-i386/atomic.h~detect-atomic-counter-underflows include/asm-i386/atomic.h
    --- 25/include/asm-i386/atomic.h~detect-atomic-counter-underflows Wed Nov 3 15:27:37 2004
    +++ 25-akpm/include/asm-i386/atomic.h Wed Nov 3 15:27:37 2004
    @@ -132,6 +132,10 @@ static __inline__ int atomic_dec_and_tes
    {
    unsigned char c;

    + if (!atomic_read(v)) {
    + printk("BUG: atomic counter underflow at:\n");
    + dump_stack();
    + }
    __asm__ __volatile__(
    LOCK "decl %0; sete %1"
    :"=m" (v->counter), "=qm" (c)
    _
    -
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