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    SubjectRe: [PATCH 7/7] lockdep: Remove cmpxchg to update nr_chain_hlocks
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    On Thu, Apr 21, 2011 at 9:42 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
    > From: Steven Rostedt <srostedt@redhat.com>
    >
    > For some reason nr_chain_hlocks is updated with cmpxchg, but this
    > is performed inside of the lockdep global "grab_lock()", which also
    > makes simple modification of this variable atomic.
    >
    > Remove the cmpxchg logic for updating nr_chain_hlocks and simplify
    > the code.
    >
    > Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    > ---
    >  kernel/lockdep.c |   14 ++++----------
    >  1 files changed, 4 insertions(+), 10 deletions(-)
    >
    > diff --git a/kernel/lockdep.c b/kernel/lockdep.c
    > index 3b1ac92..60bce52 100644
    > --- a/kernel/lockdep.c
    > +++ b/kernel/lockdep.c
    > @@ -1973,7 +1973,7 @@ static inline int lookup_chain_cache(struct task_struct *curr,
    >        struct list_head *hash_head = chainhashentry(chain_key);
    >        struct lock_chain *chain;
    >        struct held_lock *hlock_curr, *hlock_next;

    Maybe we can also remove hlock_next in this function for some cleanup, because
    it's just an alias of hlock.

    Thanks,
    Yong

    > -       int i, j, n, cn;
    > +       int i, j;
    >
    >        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
    >                return 0;
    > @@ -2033,15 +2033,9 @@ cache_hit:
    >        }
    >        i++;
    >        chain->depth = curr->lockdep_depth + 1 - i;
    > -       cn = nr_chain_hlocks;
    > -       while (cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS) {
    > -               n = cmpxchg(&nr_chain_hlocks, cn, cn + chain->depth);
    > -               if (n == cn)
    > -                       break;
    > -               cn = n;
    > -       }
    > -       if (likely(cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
    > -               chain->base = cn;
    > +       if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
    > +               chain->base = nr_chain_hlocks;
    > +               nr_chain_hlocks += chain->depth;
    >                for (j = 0; j < chain->depth - 1; j++, i++) {
    >                        int lock_id = curr->held_locks[i].class_idx - 1;
    >                        chain_hlocks[chain->base + j] = lock_id;
    > --
    > 1.7.2.3
    >
    >
    > --
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