cifs: don't use vfsmount to pin superblock for oplock breaks

Filesystems aren't really supposed to do anything with a vfsmount. It's
considered a layering violation since vfsmounts are entirely managed at
the VFS layer.

CIFS currently keeps an active reference to a vfsmount in order to
prevent the superblock vanishing before an oplock break has completed.
What we really want to do instead is to keep sb->s_active high until the
oplock break has completed. This patch borrows the scheme that NFS uses
for handling sillyrenames.

An atomic_t is added to the cifs_sb_info. When it transitions from 0 to
1, an extra reference to the superblock is taken (by bumping the
s_active value). When it transitions from 1 to 0, that reference is
dropped and a the superblock teardown may proceed if there are no more
references to it.

Also, the vfsmount pointer is removed from cifsFileInfo and from
cifs_new_fileinfo, and some bogus forward declarations are removed from
cifsfs.h.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Suresh Jayaraman <sjayaraman@suse.de>
Acked-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index c302b9c52644..fd78a355f634 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -282,7 +282,6 @@ int cifs_open(struct inode *inode, struct file *file)
                         }
 
                         pCifsFile = cifs_new_fileinfo(inode, netfid, file,
-                                                        file->f_path.mnt,
                                                         tlink, oflags, oplock);
                         if (pCifsFile == NULL) {
                                 CIFSSMBClose(xid, tcon, netfid);
@@ -375,8 +374,8 @@ int cifs_open(struct inode *inode, struct file *file)
         if (rc != 0)
                 goto out;
 
-        pCifsFile = cifs_new_fileinfo(inode, netfid, file, file->f_path.mnt,
-                                        tlink, file->f_flags, oplock);
+        pCifsFile = cifs_new_fileinfo(inode, netfid, file, tlink,
+                                        file->f_flags, oplock);
         if (pCifsFile == NULL) {
                 rc = -ENOMEM;
                 goto out;
@@ -2381,14 +2380,14 @@ void cifs_oplock_break(struct work_struct *work)
 
 void cifs_oplock_break_get(struct cifsFileInfo *cfile)
 {
-        mntget(cfile->mnt);
+        cifs_sb_active(cfile->dentry->d_sb);
         cifsFileInfo_get(cfile);
 }
 
 void cifs_oplock_break_put(struct cifsFileInfo *cfile)
 {
-        mntput(cfile->mnt);
         cifsFileInfo_put(cfile);
+        cifs_sb_deactive(cfile->dentry->d_sb);
 }
 
 const struct address_space_operations cifs_addr_ops = {