[PATCH v2 2/2] locks: ensure vfs_test_lock() never returns FILE_LOCK_DEFERRED

[NeilBrown <neilb@ownmail.net>]

From: NeilBrown <neil@brown.name>

FILE_LOCK_DEFERRED can be returned when creating or removing a lock, but
not when testing for a lock.  This support was explicitly removed in
Commit 09802fd2a8ca ("lockd: rip out deferred lock handling from testlock codepath")

However the test in nlmsvc_testlock() suggests that it *can* be returned,
only nlm cannot handle it.

To aid clarity, remove the test and instead put a similar test and
warning in vfs_test_lock().  If the impossible happens, convert
FILE_LOCK_DEFERRED to -EIO.

Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/lockd/svclock.c |  4 ----
 fs/locks.c         | 17 ++++++++++++++---
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index d66e82851599..dfd1a12b7887 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -635,10 +635,6 @@ nlmsvc_testlock(struct svc_rqst *rqstp, struct nlm_file *file,
 	conflock->fl.c.flc_owner = lock->fl.c.flc_owner;
 	error = vfs_test_lock(file->f_file[mode], &conflock->fl);
 	if (error) {
-		/* We can't currently deal with deferred test requests */
-		if (error == FILE_LOCK_DEFERRED)
-			WARN_ON_ONCE(1);
-
 		ret = nlm_lck_denied_nolocks;
 		goto out;
 	}
diff --git a/fs/locks.c b/fs/locks.c
index bf5e0d05a026..b5a3bb8790f3 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2199,12 +2199,23 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
  */
 int vfs_test_lock(struct file *filp, struct file_lock *fl)
 {
+	int error = 0;
+
 	WARN_ON_ONCE(fl->fl_ops || fl->fl_lmops);
 	WARN_ON_ONCE(filp != fl->c.flc_file);
 	if (filp->f_op->lock)
-		return filp->f_op->lock(filp, F_GETLK, fl);
-	posix_test_lock(filp, fl);
-	return 0;
+		error = filp->f_op->lock(filp, F_GETLK, fl);
+	else
+		posix_test_lock(filp, fl);
+
+	/*
+	 * We don't expect FILE_LOCK_DEFERRED and callers cannot
+	 * handle it.
+	 */
+	if (WARN_ON_ONCE(error == FILE_LOCK_DEFERRED))
+		error = -EIO;
+
+	return error;
 }
 EXPORT_SYMBOL_GPL(vfs_test_lock);
 
-- 
2.50.0.107.gf914562f5916.dirty