fs: fix do_mount_root() false positive kmemcheck warning

This false positive is due to the fact that do_mount_root() fakes a
mount option (which is normally read from userspace), and the kernel
unconditionally reads a whole page for the mount option.

Hide the false positive by using the new __getname_gfp() with the
__GFP_NOTRACK_FALSE_POSITIVE flag.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>

init/do_mounts.c

@@ -231,7 +231,8 @@ static int __init do_mount_root(char *name, char *fs, int flags, void *data)
 
 void __init mount_block_root(char *name, int flags)
 {
-	char *fs_names = __getname();
+	char *fs_names = __getname_gfp(GFP_KERNEL
+		| __GFP_NOTRACK_FALSE_POSITIVE);
 	char *p;
 #ifdef CONFIG_BLOCK
 	char b[BDEVNAME_SIZE];