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    SubjectRe: [patch] lockdep: fix possible races while disabling lock-debugging
    On Thu, Dec 07, 2006 at 02:29:03PM +0100, Ingo Molnar wrote:
    > Subject: [patch] lockdep: fix possible races while disabling lock-debugging
    > From: Ingo Molnar <mingo@elte.hu>
    ...
    > (also note that as we all know the Linux kernel is, by definition,
    > bug-free and perfect, so this code never triggers, so these fixes are
    > highly theoretical. I wrote this patch for aesthetic reasons alone.)

    Now it's too sexy! I can't work.

    PS: I had some problems with patching - probably
    because of something from -mm, but:

    > Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ...
    > @@ -567,12 +601,10 @@ static noinline int print_circular_bug_t
    > if (debug_locks_silent)
    > return 0;
    >
    > - /* hash_lock unlocked by the header */
    > - __raw_spin_lock(&hash_lock);
    > this.class = check_source->class;
    > if (!save_trace(&this.trace))
    > return 0;
    > - __raw_spin_unlock(&hash_lock);
    > +

    IMHO lock is needed here for save_trace.

    ...
    > @@ -1212,7 +1244,8 @@ register_lock_class(struct lockdep_map *
    > hash_head = classhashentry(key);
    >
    > raw_local_irq_save(flags);
    > - __raw_spin_lock(&hash_lock);
    > + if (!graph_lock())

    ! raw_local_irq_restore(flags);

    > + return NULL;
    > /*
    > * We have to do the hash-walk again, to avoid races
    > * with another CPU:

    Jarek P.
    -
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