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, 10 insertions, 2 deletions

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index b7431afdd76..070bf1aecd2 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -514,22 +514,30 @@ cifs_get_sb(struct file_system_type *fs_type,
             int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 {
         int rc;
-        struct super_block *sb = sget(fs_type, NULL, set_anon_super, NULL);
+        struct super_block *sb;
+
+        lock_kernel();
+
+        sb = sget(fs_type, NULL, set_anon_super, NULL);
 
         cFYI(1, "Devname: %s flags: %d ", dev_name, flags);
 
-        if (IS_ERR(sb))
+        if (IS_ERR(sb)) {
+                unlock_kernel();
                 return PTR_ERR(sb);
+        }
 
         sb->s_flags = flags;
 
         rc = cifs_read_super(sb, data, dev_name, flags & MS_SILENT ? 1 : 0);
         if (rc) {
                 deactivate_locked_super(sb);
+                unlock_kernel();
                 return rc;
         }
         sb->s_flags |= MS_ACTIVE;
         simple_set_mnt(mnt, sb);
+        unlock_kernel();
         return 0;
 }