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    Subject[PATCH] lockdep: fix mismatched lockdep_depth/curr_chain_hash
    Date
    Hi Greg,
    Here is the backported version of the patch. I applied it on top of
    2.6.22.10. Let me know if you have any issues.

    -Greg

    ------------------------------
    lockdep: fix mismatched lockdep_depth/curr_chain_hash

    It is possible for the current->curr_chain_key to become inconsistent with the
    current index if the chain fails to validate. The end result is that future
    lock_acquire() operations may inadvertently fail to find a hit in the cache
    resulting in a new node being added to the graph for every acquire.

    [ peterz: this might explain some of the lockdep is so _slow_ complaints. ]
    [ mingo: this does not impact the correctness of validation, but may slow
    down future operations significantly, if the chain gets very long. ]

    Signed-off-by: Gregory Haskins <ghaskins@novell.com>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---

    kernel/lockdep.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/kernel/lockdep.c b/kernel/lockdep.c
    index 1a5ff22..072cf25 100644
    --- a/kernel/lockdep.c
    +++ b/kernel/lockdep.c
    @@ -2166,7 +2166,6 @@ out_calc_hash:
    }
    #endif
    chain_key = iterate_chain_key(chain_key, id);
    - curr->curr_chain_key = chain_key;

    /*
    * Trylock needs to maintain the stack of held locks, but it
    @@ -2215,6 +2214,7 @@ out_calc_hash:
    if (unlikely(!debug_locks))
    return 0;

    + curr->curr_chain_key = chain_key;
    curr->lockdep_depth++;
    check_chain_key(curr);
    #ifdef CONFIG_DEBUG_LOCKDEP
    -
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