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, 4 insertions, 0 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c9483d8f6140..a7ba3bccadc5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1430,6 +1430,8 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
         struct super_block *sb;
         struct cgroupfs_root *new_root;
 
+        lock_kernel();
+
         /* First find the desired set of subsystems */
         mutex_lock(&cgroup_mutex);
         ret = parse_cgroupfs_options(data, &opts);
@@ -1559,6 +1561,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
         simple_set_mnt(mnt, sb);
         kfree(opts.release_agent);
         kfree(opts.name);
+        unlock_kernel();
         return 0;
 
  drop_new_super:
@@ -1568,6 +1571,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
  out_err:
         kfree(opts.release_agent);
         kfree(opts.name);
+        unlock_kernel();
 
         return ret;
 }