Re: [PATCH 3/5] cifsd: add file operations

On (21/03/22 07:02), Al Viro wrote:

On Mon, Mar 22, 2021 at 02:13:42PM +0900, Namjae Jeon wrote:

quoted

+static struct ksmbd_file *__ksmbd_lookup_fd(struct ksmbd_file_table *ft,
+					    unsigned int id)
+{
+	bool unclaimed = true;
+	struct ksmbd_file *fp;
+
+	read_lock(&ft->lock);
+	fp = idr_find(ft->idr, id);
+	if (fp)
+		fp = ksmbd_fp_get(fp);
+
+	if (fp && fp->f_ci) {
+		read_lock(&fp->f_ci->m_lock);
+		unclaimed = list_empty(&fp->node);
+		read_unlock(&fp->f_ci->m_lock);
+	}
+	read_unlock(&ft->lock);
+
+	if (fp && unclaimed) {
+		atomic_dec(&fp->refcount);
+		return NULL;
+	}

Can that atomic_dec() end up dropping the last remaining reference?

Yes, I think it should increment refcount only for "claimed" fp.