[PATCH RFC v13 2/4] fs/lock: add new callback, lm_lock_expired, to lock_manager_operations

[Dai Ngo <dai.ngo@oracle.com>]

Add new callback, lm_lock_expired, to lock_manager_operations to allow
the lock manager to take appropriate action to resolve the lock conflict
if possible. The callback takes 1 argument, the file_lock of the blocker
and returns true if the conflict was resolved else returns false. Note
that the lock manager has to be able to resolve the conflict while
the spinlock flc_lock is held.

Lock manager, such as NFSv4 courteous server, uses this callback to
resolve conflict by destroying lock owner, or the NFSv4 courtesy client
(client that has expired but allowed to maintains its states) that owns
the lock.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 Documentation/filesystems/locking.rst |  2 ++
 fs/locks.c                            | 14 ++++++++++----
 include/linux/fs.h                    |  1 +
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index aaca0b601819..ebd73e76cb7e 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -434,6 +434,7 @@ prototypes::
 	void (*lm_break)(struct file_lock *); /* break_lease callback */
 	int (*lm_change)(struct file_lock **, int);
 	bool (*lm_breaker_owns_lease)(struct file_lock *);
+	bool (*lm_lock_expired)(struct file_lock *);
 
 locking rules:
 
@@ -445,6 +446,7 @@ lm_grant:		no		no			no
 lm_break:		yes		no			no
 lm_change		yes		no			no
 lm_breaker_owns_lease:	yes     	no			no
+lm_lock_expired 	yes     	no			no
 ======================	=============	=================	=========
 
 buffer_head
diff --git a/fs/locks.c b/fs/locks.c
index 8c6df10cd9ed..52ede42651df 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -883,10 +883,13 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
 
 	spin_lock(&ctx->flc_lock);
 	list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
-		if (posix_locks_conflict(fl, cfl)) {
-			locks_copy_conflock(fl, cfl);
-			goto out;
-		}
+		if (!posix_locks_conflict(fl, cfl))
+			continue;
+		if (cfl->fl_lmops && cfl->fl_lmops->lm_lock_expired &&
+			cfl->fl_lmops->lm_lock_expired(cfl))
+			continue;
+		locks_copy_conflock(fl, cfl);
+		goto out;
 	}
 	fl->fl_type = F_UNLCK;
 out:
@@ -1089,6 +1092,9 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 		list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
 			if (!posix_locks_conflict(request, fl))
 				continue;
+			if (fl->fl_lmops && fl->fl_lmops->lm_lock_expired &&
+				fl->fl_lmops->lm_lock_expired(fl))
+				continue;
 			if (conflock)
 				locks_copy_conflock(conflock, fl);
 			error = -EAGAIN;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e2d892b201b0..831b20430d6e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1062,6 +1062,7 @@ struct lock_manager_operations {
 	int (*lm_change)(struct file_lock *, int, struct list_head *);
 	void (*lm_setup)(struct file_lock *, void **);
 	bool (*lm_breaker_owns_lease)(struct file_lock *);
+	bool (*lm_lock_expired)(struct file_lock *cfl);
 };
 
 struct lock_manager {
-- 
2.9.5