BKL: Explicitly add BKL around get_sb/fill_super

This patch is a preparation necessary to remove the BKL from do_new_mount().
It explicitly adds calls to lock_kernel()/unlock_kernel() around
get_sb/fill_super operations for filesystems that still uses the BKL.

I've read through all the code formerly covered by the BKL inside
do_kern_mount() and have satisfied myself that it doesn't need the BKL
any more.

do_kern_mount() is already called without the BKL when mounting the rootfs
and in nfsctl. do_kern_mount() calls vfs_kern_mount(), which is called
from various places without BKL: simple_pin_fs(), nfs_do_clone_mount()
through nfs_follow_mountpoint(), afs_mntpt_do_automount() through
afs_mntpt_follow_link(). Both later functions are actually the filesystems
follow_link inode operation. vfs_kern_mount() is calling the specified
get_sb function and lets the filesystem do its job by calling the given
fill_super function.

Therefore I think it is safe to push down the BKL from the VFS to the
low-level filesystems get_sb/fill_super operation.

[arnd: do not add the BKL to those file systems that already
       don't use it elsewhere]

Signed-off-by: Jan Blunck <jblunck@infradead.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Christoph Hellwig <hch@infradead.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index bbc94ae4fd7..e2b0b978340 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -9,6 +9,7 @@
 #include <linux/module.h>
 #include <linux/time.h>
 #include <linux/buffer_head.h>
+#include <linux/smp_lock.h>     /* For lock_kernel() */
 #include "fat.h"
 
 /* Characters that are undesirable in an MS-DOS file name */
@@ -662,12 +663,16 @@ static int msdos_fill_super(struct super_block *sb, void *data, int silent)
 {
 	int res;
 
+	lock_kernel();
 	res = fat_fill_super(sb, data, silent, &msdos_dir_inode_operations, 0);
-	if (res)
+	if (res) {
+		unlock_kernel();
 		return res;
+	}
 
 	sb->s_flags |= MS_NOATIME;
 	sb->s_root->d_op = &msdos_dentry_operations;
+	unlock_kernel();
 	return 0;
 }