2 files changed, 17 insertions, 2 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 1ad29c9b6252..50cb0a2b74d9 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -725,6 +725,10 @@ next_task:
 /* Try to create a FLOCK lock on filp. We always insert new FLOCK locks
  * at the head of the list, but that's secret knowledge known only to
  * flock_lock_file and posix_lock_file.
+ *
+ * Note that if called with an FL_EXISTS argument, the caller may determine
+ * whether or not a lock was successfully freed by testing the return
+ * value for -ENOENT.
  */
 static int flock_lock_file(struct file *filp, struct file_lock *request)
 {
@@ -750,8 +754,11 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
                 break;
         }
 
-        if (request->fl_type == F_UNLCK)
+        if (request->fl_type == F_UNLCK) {
+                if ((request->fl_flags & FL_EXISTS) && !found)
+                        error = -ENOENT;
                 goto out;
+        }
 
         error = -ENOMEM;
         new_fl = locks_alloc_lock();
@@ -948,8 +955,11 @@ static int __posix_lock_file_conf(struct inode *inode, struct file_lock *request
 
         error = 0;
         if (!added) {
-                if (request->fl_type == F_UNLCK)
+                if (request->fl_type == F_UNLCK) {
+                        if (request->fl_flags & FL_EXISTS)
+                                error = -ENOENT;
                         goto out;
+                }
 
                 if (!new_fl) {
                         error = -ENOLCK;
@@ -996,6 +1006,10 @@ static int __posix_lock_file_conf(struct inode *inode, struct file_lock *request
  * Add a POSIX style lock to a file.
  * We merge adjacent & overlapping locks whenever possible.
  * POSIX locks are sorted by owner task, then by starting address
+ *
+ * Note that if called with an FL_EXISTS argument, the caller may determine
+ * whether or not a lock was successfully freed by testing the return
+ * value for -ENOENT.
  */
 int posix_lock_file(struct file *filp, struct file_lock *fl)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 134b32068246..43aef9b230fd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -716,6 +716,7 @@ extern spinlock_t files_lock;
 #define FL_POSIX        1
 #define FL_FLOCK        2
 #define FL_ACCESS       8       /* not trying to lock, just looking */
+#define FL_EXISTS       16      /* when unlocking, test for existence */
 #define FL_LEASE        32      /* lease held on this file */
 #define FL_CLOSE        64      /* unlock on close */
 #define FL_SLEEP        128     /* A blocking lock */