locks: make locks_mandatory_area check for file-private locks

Allow locks_mandatory_area() to handle file-private locks correctly.
If there is a file-private lock set on an open file and we're doing I/O
via the same, then that should not cause anything to block.

Handle this by first doing a non-blocking FL_ACCESS check for a
file-private lock, and then fall back to checking for a classic POSIX
lock (and possibly blocking).

Note that this approach is subject to the same races that have always
plagued mandatory locking on Linux.

Reported-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>

diff --git a/fs/locks.c b/fs/locks.c
index d82c51c4fcd22d0a44b78f3274676c25a8bbbdff..13fc7a6d380ae6648945c8956cc53901de2d0ccc 100644 (file)
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1199,19 +1199,30 @@ int locks_mandatory_area(int read_write, struct inode *inode,
 {
        struct file_lock fl;
        int error;
+       bool sleep = false;
 
        locks_init_lock(&fl);
-       fl.fl_owner = current->files;
        fl.fl_pid = current->tgid;
        fl.fl_file = filp;
        fl.fl_flags = FL_POSIX | FL_ACCESS;
        if (filp && !(filp->f_flags & O_NONBLOCK))
-               fl.fl_flags |= FL_SLEEP;
+               sleep = true;
        fl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
        fl.fl_start = offset;
        fl.fl_end = offset + count - 1;
 
        for (;;) {
+               if (filp) {
+                       fl.fl_owner = (fl_owner_t)filp;
+                       fl.fl_flags &= ~FL_SLEEP;
+                       error = __posix_lock_file(inode, &fl, NULL);
+                       if (!error)
+                               break;
+               }
+
+               if (sleep)
+                       fl.fl_flags |= FL_SLEEP;
+               fl.fl_owner = current->files;
                error = __posix_lock_file(inode, &fl, NULL);
                if (error != FILE_LOCK_DEFERRED)
                        break;