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Subject[PATCH 3/5] locking/lockdep: Add a faster path in __lock_release()
Date
When __lock_release() is called, the most likely unlock scenario is
on the innermost lock in the chain. In this case, we can skip some of
the checks and provide a faster path to completion.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/lockdep.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index add0468..ca002c0 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3625,6 +3625,13 @@ static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
curr->lockdep_depth = i;
curr->curr_chain_key = hlock->prev_chain_key;

+ /*
+ * The most likely case is when the unlock is on the innermost
+ * lock. In this case, we are done!
+ */
+ if (i == depth - 1)
+ return 1;
+
if (reacquire_held_locks(curr, depth, i + 1))
return 0;

@@ -3632,10 +3639,14 @@ static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
* We had N bottles of beer on the wall, we drank one, but now
* there's not N-1 bottles of beer left on the wall...
*/
- if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1))
- return 0;
+ DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1);

- return 1;
+ /*
+ * Since reacquire_held_locks() would have called check_chain_key()
+ * indirectly via __lock_acquire(), we don't need to do it again
+ * on return.
+ */
+ return 0;
}

static int __lock_is_held(const struct lockdep_map *lock, int read)
--
1.8.3.1
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