[Cluster-devel] [PATCH 2/7] lockd: don't call vfs_lock_file() for pending requests

[Alexander Aring]

This patch returns nlm_lck_blocked in nlmsvc_lock() when an asynchronous
lock request is pending. During testing I ran into the case with the
side-effects that lockd is waiting for only one lm_grant() callback
because it's already part of the nlm_blocked list. If another
asynchronous for the same nlm_block is triggered two lm_grant()
callbacks will occur but lockd was only waiting for one.

To avoid any change of existing users this handling will only being made
when export_op_support_safe_async_lock() returns true.

Signed-off-by: Alexander Aring <aahringo at redhat.com>
---
 fs/lockd/svclock.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index 6e3b230e8317..aa4174fbaf5b 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -531,6 +531,23 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 		goto out;
 	}
 
+	spin_lock(&nlm_blocked_lock);
+	/*
+	 * If this is a lock request for an already pending
+	 * lock request we return nlm_lck_blocked without calling
+	 * vfs_lock_file() again. Otherwise we have two pending
+	 * requests on the underlaying ->lock() implementation but
+	 * only one nlm_block to being granted by lm_grant().
+	 */
+	if (export_op_support_safe_async_lock(inode->i_sb->s_export_op,
+					      nlmsvc_file_file(file)->f_op) &&
+	    !list_empty(&block->b_list)) {
+		spin_unlock(&nlm_blocked_lock);
+		ret = nlm_lck_blocked;
+		goto out;
+	}
+	spin_unlock(&nlm_blocked_lock);
+
 	if (!wait)
 		lock->fl.fl_flags &= ~FL_SLEEP;
 	mode = lock_to_openmode(&lock->fl);
@@ -543,13 +560,6 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 			ret = nlm_granted;
 			goto out;
 		case -EAGAIN:
-			/*
-			 * If this is a blocking request for an
-			 * already pending lock request then we need
-			 * to put it back on lockd's block list
-			 */
-			if (wait)
-				break;
 			ret = async_block ? nlm_lck_blocked : nlm_lck_denied;
 			goto out;
 		case FILE_LOCK_DEFERRED:
-- 
2.31.1