cifs: use a refcount to protect open/closing the cached file handle

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Cc: <stable@vger.kernel.org>

fs/cifs/cifsglob.h

@@ -907,6 +907,7 @@ cap_unix(struct cifs_ses *ses)
 
 struct cached_fid {
 	bool is_valid:1;	/* Do we have a useable root fid */
+	struct kref refcount;
 	struct cifs_fid *fid;
 	struct mutex fid_mutex;
 	struct cifs_tcon *tcon;

fs/cifs/smb2inode.c

@@ -120,7 +120,9 @@ smb2_open_op_close(const unsigned int xid, struct cifs_tcon *tcon,
 		break;
 	}
 
-	if (use_cached_root_handle == false)
+	if (use_cached_root_handle)
+		close_shroot(&tcon->crfid);
+	else
 		rc = SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
 	if (tmprc)
 		rc = tmprc;

fs/cifs/smb2ops.c

@@ -470,21 +470,36 @@ SMB3_request_interfaces(const unsigned int xid, struct cifs_tcon *tcon)
 	return rc;
 }
 
-void
-smb2_cached_lease_break(struct work_struct *work)
+static void
+smb2_close_cached_fid(struct kref *ref)
 {
-	struct cached_fid *cfid = container_of(work,
-				struct cached_fid, lease_break);
-	mutex_lock(&cfid->fid_mutex);
+	struct cached_fid *cfid = container_of(ref, struct cached_fid,
+					       refcount);
+
 	if (cfid->is_valid) {
 		cifs_dbg(FYI, "clear cached root file handle\n");
 		SMB2_close(0, cfid->tcon, cfid->fid->persistent_fid,
 			   cfid->fid->volatile_fid);
 		cfid->is_valid = false;
 	}
+}
+
+void close_shroot(struct cached_fid *cfid)
+{
+	mutex_lock(&cfid->fid_mutex);
+	kref_put(&cfid->refcount, smb2_close_cached_fid);
 	mutex_unlock(&cfid->fid_mutex);
 }
 
+void
+smb2_cached_lease_break(struct work_struct *work)
+{
+	struct cached_fid *cfid = container_of(work,
+				struct cached_fid, lease_break);
+
+	close_shroot(cfid);
+}
+
 /*
  * Open the directory at the root of a share
  */
@@ -499,6 +514,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 	if (tcon->crfid.is_valid) {
 		cifs_dbg(FYI, "found a cached root file handle\n");
 		memcpy(pfid, tcon->crfid.fid, sizeof(struct cifs_fid));
+		kref_get(&tcon->crfid.refcount);
 		mutex_unlock(&tcon->crfid.fid_mutex);
 		return 0;
 	}
@@ -515,6 +531,8 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 		memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
 		tcon->crfid.tcon = tcon;
 		tcon->crfid.is_valid = true;
+		kref_init(&tcon->crfid.refcount);
+		kref_get(&tcon->crfid.refcount);
 	}
 	mutex_unlock(&tcon->crfid.fid_mutex);
 	return rc;
@@ -558,6 +576,9 @@ smb3_qfs_tcon(const unsigned int xid, struct cifs_tcon *tcon)
 			FS_SECTOR_SIZE_INFORMATION); /* SMB3 specific */
 	if (no_cached_open)
 		SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
+	else
+		close_shroot(&tcon->crfid);
+
 	return;
 }
 

fs/cifs/smb2proto.h

@@ -68,6 +68,7 @@ extern int smb3_handle_read_data(struct TCP_Server_Info *server,
 
 extern int open_shroot(unsigned int xid, struct cifs_tcon *tcon,
 			struct cifs_fid *pfid);
+extern void close_shroot(struct cached_fid *cfid);
 extern void move_smb2_info_to_cifs(FILE_ALL_INFO *dst,
 				   struct smb2_file_all_info *src);
 extern int smb2_query_path_info(const unsigned int xid, struct cifs_tcon *tcon,