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From:   Dai Ngo <dai.ngo@oracle.com>
To:     bfields@fieldses.org
Cc:     chuck.lever@oracle.com, linux-nfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: [PATCH RFC 1/2] fs/lock: add new callback, lm_expire_lock, to lock_manager_operations.
Date:   Sat,  3 Jul 2021 00:34:19 -0400
Message-Id: <20210703043420.84549-2-dai.ngo@oracle.com>
In-Reply-To: <20210703043420.84549-1-dai.ngo@oracle.com>
References: <20210703043420.84549-1-dai.ngo@oracle.com>
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Add new callback, lm_expire_lock, to lock_manager_operations to allow
the lock manager to take appropriate action to resolve the lock conflict
if possible. The callback takes 2 arguments, file_lock of the blocker
and a testonly flag:

testonly = 1  check and return true if lock conflict can be resolved
              else return false.
testonly = 0  resolve the conflict if possible, return true if conflict
              was resolved esle return false.

Lock manager, such as NFSv4 courteous server, can use 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>
---
 fs/locks.c         | 10 ++++++++++
 include/linux/fs.h |  1 +
 2 files changed, 11 insertions(+)

diff --git a/fs/locks.c b/fs/locks.c
index 74b2a1dfe8d8..d712fe2ee530 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1140,6 +1140,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 	int error;
 	bool added = false;
 	LIST_HEAD(dispose);
+	bool ret;
 
 	ctx = locks_get_lock_context(inode, request->fl_type);
 	if (!ctx)
@@ -1166,9 +1167,18 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 	 * blocker's list of waiters and the global blocked_hash.
 	 */
 	if (request->fl_type != F_UNLCK) {
+retry:
 		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_expire_lock &&
+					fl->fl_lmops->lm_expire_lock(fl, 1)) {
+				spin_unlock(&ctx->flc_lock);
+				ret = fl->fl_lmops->lm_expire_lock(fl, 0);
+				spin_lock(&ctx->flc_lock);
+				if (ret)
+					goto retry;
+			}
 			if (conflock)
 				locks_copy_conflock(conflock, fl);
 			error = -EAGAIN;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c3c88fdb9b2a..ee7407f64e27 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1025,6 +1025,7 @@ 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_expire_lock)(struct file_lock *fl, bool testonly);
 };
 
 struct lock_manager {
-- 
2.9.5