Ocfs2: Handle empty list in lockres_seq_start() for dlmdebug.c

This patch tries to handle the case in which list 'dlm->tracking_list' is
empty, to avoid accessing an invalid pointer. It fixes the following oops:

http://oss.oracle.com/bugzilla/show_bug.cgi?id=1287

Signed-off-by: Tristan Ye <tristan.ye@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

diff --git a/fs/ocfs2/dlm/dlmdebug.c b/fs/ocfs2/dlm/dlmdebug.c
index 5efdd37dfe484f2f6207ac2c7c6927fda0cc1ea0..901ca52bf86b293639ea39c8e1f460b66bc1f265 100644 (file)
--- a/fs/ocfs2/dlm/dlmdebug.c
+++ b/fs/ocfs2/dlm/dlmdebug.c
@@ -636,8 +636,14 @@ static void *lockres_seq_start(struct seq_file *m, loff_t *pos)
        spin_lock(&dlm->track_lock);
        if (oldres)
                track_list = &oldres->tracking;
-       else
+       else {
                track_list = &dlm->tracking_list;
+               if (list_empty(track_list)) {
+                       dl = NULL;
+                       spin_unlock(&dlm->track_lock);
+                       goto bail;
+               }
+       }
 
        list_for_each_entry(res, track_list, tracking) {
                if (&res->tracking == &dlm->tracking_list)
@@ -660,6 +666,7 @@ static void *lockres_seq_start(struct seq_file *m, loff_t *pos)
        } else
                dl = NULL;
 
+bail:
        /* passed to seq_show */
        return dl;
 }