fs: cleanup files_lock locking

fs: cleanup files_lock locking

Lock tty_files with a new spinlock, tty_files_lock; provide helpers to
manipulate the per-sb files list; unexport the files_lock spinlock.

Cc: linux-kernel@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 42043f9..bd7da0f 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2170,7 +2170,7 @@
 
 	tty = get_current_tty();
 	if (tty) {
-		file_list_lock();
+		spin_lock(&tty_files_lock);
 		if (!list_empty(&tty->tty_files)) {
 			struct inode *inode;
 
@@ -2186,7 +2186,7 @@
 				drop_tty = 1;
 			}
 		}
-		file_list_unlock();
+		spin_unlock(&tty_files_lock);
 		tty_kref_put(tty);
 	}
 	/* Reset controlling tty. */