locks: fix F_GETLK regression (failure to find conflicts)

In 9d6a8c5c21 we changed posix_test_lock
to modify its single file_lock argument instead of taking separate input
and output arguments.  This makes it no longer safe to set the output
lock's fl_type to F_UNLCK before looking for a conflict, since that
means searching for a conflict against a lock with type F_UNLCK.

This fixes a regression which causes F_GETLK to incorrectly report no
conflict on most filesystems (including any filesystem that doesn't do
its own locking).

Also fix posix_lock_to_flock() to copy the lock type.  This isn't
strictly necessary, since the caller already does this; but it seems
less likely to cause confusion in the future.

Thanks to Doug Chapman for the bug report.

Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Acked-by: Doug Chapman <doug.chapman@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/locks.c

@@ -669,7 +669,6 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
 {
 	struct file_lock *cfl;
 
-	fl->fl_type = F_UNLCK;
 	lock_kernel();
 	for (cfl = filp->f_path.dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
 		if (!IS_POSIX(cfl))
@@ -681,7 +680,8 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
 		__locks_copy_lock(fl, cfl);
 		unlock_kernel();
 		return 1;
-	}
+	} else
+		fl->fl_type = F_UNLCK;
 	unlock_kernel();
 	return 0;
 }
@@ -1632,6 +1632,7 @@ static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
 	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
 		fl->fl_end - fl->fl_start + 1;
 	flock->l_whence = 0;
+	flock->l_type = fl->fl_type;
 	return 0;
 }