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

[ Upstream commit b1432a2a35565f538586774a03bf277c27fc267d ]

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 215e41abf101a1e70afbe2b151980ed237a632a0..9ec1eea7c3a33497bafd184edbe6a0fd4632b395 100644 (file)
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -765,6 +765,19 @@ 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);