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 <jlayton@xxxxxxxxxx>
---
fs/locks.c | 17 ++++++++++++++---
1 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/fs/locks.c b/fs/locks.c
index 8f56651..a8f3b33 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -532,7 +532,10 @@ 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)
@@ -560,8 +563,16 @@ 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.
+ */
+ if (list_empty(&blocker->fl_block))
+ return;
+
spin_lock(&file_lock_lock);
- while (!list_empty(&blocker->fl_block)) {
+ do {
struct file_lock *waiter;
waiter = list_first_entry(&blocker->fl_block,
@@ -571,7 +582,7 @@ static void locks_wake_up_blocks(struct file_lock *blocker)
waiter->fl_lmops->lm_notify(waiter);
else
wake_up(&waiter->fl_wait);
- }
+ } while (!list_empty(&blocker->fl_block));
spin_unlock(&file_lock_lock);
}
--
1.7.1
--
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