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    SubjectRe: 2.6.9-rc3-mm2
    On Tue, 5 Oct 2004, Peter Zijlstra wrote:
    > On Mon, 2004-10-04 at 19:13, Pasi Savolainen wrote:
    > > LD .tmp_vmlinux1
    > > KSYM .tmp_kallsyms1.S
    > > make: *** wait: No child processes. Stop.
    > > - -
    > > The 'no child processes' keeps on coming up at 'random' moments under
    > > rc3-mm1. First time ever that I've seen it otherwise.
    >
    > Just a simple mee too!
    > on 2.6.9-rc3-mm2-VP-T0 and on some earlier Sx patches as well.
    > Unfortunatly I haven't had time to track back as to when this was
    > introduced.

    Please, would you try this patch below that I posted yesterday?
    At the time I thought the trylock was hardly used so not urgent.

    I've just now discovered that the standard SMP PREEMPT read_lock
    - as in do_wait's read_lock(&tasklist_lock) for example - uses it
    via one of those dreaded expansions that grep misses:
    if (likely(_raw_##op##_trylock(lock)))

    I've been suffering the occasional leftover zombie from multiple
    kernel builds precisely since the preempt-smp.patch went in; been
    hunting it unsuccessfully in spare moments, yesterday noticed that
    bug, today realize it's probably what I've been hunting - I'm
    about to start my own tests again, can't be sure until tomorrow.

    Hugh

    The i386 and x86_64 _raw_read_trylocks in preempt-smp.patch
    are too successful: atomic_read() returns a signed integer.

    Signed-off-by: Hugh Dickins <hugh@veritas.com>

    --- 2.6.9-rc3-mm2/include/asm-i386/spinlock.h 2004-10-04 12:00:14.000000000 +0100
    +++ linux/include/asm-i386/spinlock.h 2004-10-04 18:50:32.752864600 +0100
    @@ -235,7 +235,7 @@ static inline int _raw_read_trylock(rwlo
    {
    atomic_t *count = (atomic_t *)lock;
    atomic_dec(count);
    - if (atomic_read(count) < RW_LOCK_BIAS)
    + if (atomic_read(count) >= 0)
    return 1;
    atomic_inc(count);
    return 0;
    --- 2.6.9-rc3-mm2/include/asm-x86_64/spinlock.h 2004-10-04 12:00:15.000000000 +0100
    +++ linux/include/asm-x86_64/spinlock.h 2004-10-04 18:50:32.752864600 +0100
    @@ -236,7 +236,7 @@ static inline int _raw_read_trylock(rwlo
    {
    atomic_t *count = (atomic_t *)lock;
    atomic_dec(count);
    - if (atomic_read(count) < RW_LOCK_BIAS)
    + if (atomic_read(count) >= 0)
    return 1;
    atomic_inc(count);
    return 0;
    -
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