vfs: umount_begin BKL pushdown

Push BKL down into ->umount_begin()

Signed-off-by: Alessio Igor Bogani <abogani@texware.it>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index 5f8ab8a..7d23214 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -37,6 +37,7 @@
 #include <linux/mount.h>
 #include <linux/idr.h>
 #include <linux/sched.h>
+#include <linux/smp_lock.h>
 #include <net/9p/9p.h>
 #include <net/9p/client.h>
 
@@ -230,9 +231,12 @@
 static void
 v9fs_umount_begin(struct super_block *sb)
 {
-	struct v9fs_session_info *v9ses = sb->s_fs_info;
+	struct v9fs_session_info *v9ses;
 
+	lock_kernel();
+	v9ses = sb->s_fs_info;
 	v9fs_session_cancel(v9ses);
+	unlock_kernel();
 }
 
 static const struct super_operations v9fs_super_ops = {