ocfs2: dlm: fix race between purge and get lock resource

commit b1432a2a35565f538586774a03bf277c27fc267d upstream.

There is a race window in dlm_get_lock_resource(), which may return a
lock resource which has been purged.  This will cause the process to
hang forever in dlmlock() as the ast msg can't be handled due to its
lock resource not existing.

    dlm_get_lock_resource {
        ...
        spin_lock(&dlm->spinlock);
        tmpres = __dlm_lookup_lockres_full(dlm, lockid, namelen, hash);
        if (tmpres) {
             spin_unlock(&dlm->spinlock);
             >>>>>>>> race window, dlm_run_purge_list() may run and purge
                              the lock resource
             spin_lock(&tmpres->spinlock);
             ...
             spin_unlock(&tmpres->spinlock);
        }
    }

Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <joseph.qi@huawei.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 2b941113e42332b3e914f386e5318f690c69e6d6..2c119d5d04c9b342747207d8730a5813ec0fcd48 100644 (file)
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -729,6 +729,19 @@ lookup:
        if (tmpres) {
                spin_unlock(&dlm->spinlock);
                spin_lock(&tmpres->spinlock);
+
+               /*
+                * Right after dlm spinlock was released, dlm_thread could have
+                * purged the lockres. Check if lockres got unhashed. If so
+                * start over.
+                */
+               if (hlist_unhashed(&tmpres->hash_node)) {
+                       spin_unlock(&tmpres->spinlock);
+                       dlm_lockres_put(tmpres);
+                       tmpres = NULL;
+                       goto lookup;
+               }
+
                /* Wait on the thread that is mastering the resource */
                if (tmpres->owner == DLM_LOCK_RES_OWNER_UNKNOWN) {
                        __dlm_wait_on_lockres(tmpres);