cifs: Grab a reference for the dentry of the cached directory during the lifetime of the cache

We need to hold both a reference for the root/superblock as well as the directory that we
are caching. We need to drop these references before we call kill_anon_sb().

At this point, the root and the cached dentries are always the same but this will change
once we start caching other directories as well.
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsfs.c

@@ -257,11 +257,28 @@ cifs_read_super(struct super_block *sb)
 static void cifs_kill_sb(struct super_block *sb)
 {
 	struct cifs_sb_info *cifs_sb = CIFS_SB(sb);
+	struct cifs_tcon *tcon;
+	struct cached_fid *cfid;
 
+	/*
+	 * We ned to release all dentries for the cached directories
+	 * before we kill the sb.
+	 */
 	if (cifs_sb->root) {
 		dput(cifs_sb->root);
 		cifs_sb->root = NULL;
 	}
+	tcon = cifs_sb_master_tcon(cifs_sb);
+	if (tcon) {
+		cfid = &tcon->crfid;
+		mutex_lock(&cfid->fid_mutex);
+		if (cfid->dentry) {
+
+			dput(cfid->dentry);
+			cfid->dentry = NULL;
+		}
+		mutex_unlock(&cfid->fid_mutex);
+	}
 
 	kill_anon_super(sb);
 	cifs_umount(cifs_sb);

fs/cifs/cifsglob.h

@@ -992,6 +992,7 @@ struct cached_fid {
 	struct cifs_fid *fid;
 	struct mutex fid_mutex;
 	struct cifs_tcon *tcon;
+	struct dentry *dentry;
 	struct work_struct lease_break;
 	struct smb2_file_all_info file_all_info;
 };

fs/cifs/smb2ops.c

@@ -690,6 +690,10 @@ smb2_close_cached_fid(struct kref *ref)
 		cfid->is_valid = false;
 		cfid->file_all_info_is_valid = false;
 		cfid->has_lease = false;
+		if (cfid->dentry) {
+			dput(cfid->dentry);
+			cfid->dentry = NULL;
+		}
 	}
 }
 
@@ -747,6 +751,7 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	__le16 utf16_path = 0; /* Null - since an open of top of share */
 	u8 oplock = SMB2_OPLOCK_LEVEL_II;
 	struct cifs_fid *pfid;
+	struct dentry *dentry;
 
 	if (tcon->nohandlecache)
 		return -ENOTSUPP;
@@ -757,6 +762,8 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	if (strlen(path))
 		return -ENOENT;
 
+	dentry = cifs_sb->root;
+
 	mutex_lock(&tcon->crfid.fid_mutex);
 	if (tcon->crfid.is_valid) {
 		cifs_dbg(FYI, "found a cached root file handle\n");
@@ -881,6 +888,8 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
 	tcon->crfid.tcon = tcon;
 	tcon->crfid.is_valid = true;
+	tcon->crfid.dentry = dentry;
+	dget(dentry);
 	kref_init(&tcon->crfid.refcount);
 
 	/* BB TBD check to see if oplock level check can be removed below */