Since we always hold the i_lock when inserting a new waiter onto the fl_block list, we can avoid taking the global lock at all if we find that it's empty when we go to wake up blocked waiters.
Signed-off-by: Jeff Layton <[email protected]> --- fs/locks.c | 15 ++++++++++++++- 1 files changed, 14 insertions(+), 1 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index ce302d4..84e269f 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -548,7 +548,10 @@ static void locks_delete_block(struct file_lock *waiter) * the order they blocked. The documentation doesn't require this but * it seems like the reasonable thing to do. * - * Must be called with file_lock_lock held! + * Must be called with both the i_lock and file_lock_lock held. The fl_block + * list itself is protected by the file_lock_list, but by ensuring that the + * i_lock is also held on insertions we can avoid taking the file_lock_lock + * in some cases when we see that the fl_block list is empty. */ static void __locks_insert_block(struct file_lock *blocker, struct file_lock *waiter) @@ -576,6 +579,16 @@ static void locks_insert_block(struct file_lock *blocker, */ static void locks_wake_up_blocks(struct file_lock *blocker) { + /* + * Avoid taking global lock if list is empty. This is safe since new + * blocked requests are only added to the list under the i_lock, and + * the i_lock is always held here. Note that removal from the fl_block + * list does not require the i_lock, so we must recheck list_empty() + * after acquiring the file_lock_lock. + */ + if (list_empty(&blocker->fl_block)) + return; + spin_lock(&file_lock_lock); while (!list_empty(&blocker->fl_block)) { struct file_lock *waiter; -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
