locks: add a new "lm_owner_key" lock operation

Currently, the hashing that the locking code uses to add these values
to the blocked_hash is simply calculated using fl_owner field. That's
valid in most cases except for server-side lockd, which validates the
owner of a lock based on fl_owner and fl_pid.

In the case where you have a small number of NFS clients doing a lot
of locking between different processes, you could end up with all
the blocked requests sitting in a very small number of hash buckets.

Add a new lm_owner_key operation to the lock_manager_operations that
will generate an unsigned long to use as the key in the hashtable.
That function is only implemented for server-side lockd, and simply
XORs the fl_owner and fl_pid.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 2 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 71d847cbbb6..6242e0b1c69 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -521,10 +521,18 @@ locks_delete_global_locks(struct file_lock *fl)
 	spin_unlock(&file_lock_lock);
 }
 
+static unsigned long
+posix_owner_key(struct file_lock *fl)
+{
+	if (fl->fl_lmops && fl->fl_lmops->lm_owner_key)
+		return fl->fl_lmops->lm_owner_key(fl);
+	return (unsigned long)fl->fl_owner;
+}
+
 static inline void
 locks_insert_global_blocked(struct file_lock *waiter)
 {
-	hash_add(blocked_hash, &waiter->fl_link, (unsigned long)waiter->fl_owner);
+	hash_add(blocked_hash, &waiter->fl_link, posix_owner_key(waiter));
 }
 
 static inline void
@@ -757,7 +765,7 @@ static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
 {
 	struct file_lock *fl;
 
-	hash_for_each_possible(blocked_hash, fl, fl_link, (unsigned long)block_fl->fl_owner) {
+	hash_for_each_possible(blocked_hash, fl, fl_link, posix_owner_key(block_fl)) {
 		if (posix_same_owner(fl, block_fl))
 			return fl->fl_next;
 	}