lockd: don't call vfs_lock_file() for pending requests

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.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index d500e32ebb18bfd9ff4ec7c9d06a985d98431278..c313622a95787696132960bac49ab324c73bfade 100644 (file)
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -541,6 +541,22 @@ 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 (exportfs_lock_op_is_async(inode->i_sb->s_export_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);
@@ -553,13 +569,6 @@ 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: