From: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
Subject: ocfs2: dlm: fix race between purge and get lock resource
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@xxxxxxxxxx>
Cc: Joseph Qi <joseph.qi@xxxxxxxxxx>
Cc: Mark Fasheh <mfasheh@xxxxxxxx>
Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/ocfs2/dlm/dlmmaster.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff -puN fs/ocfs2/dlm/dlmmaster.c~ocfs2-dlm-fix-race-between-purge-and-get-lock-resource fs/ocfs2/dlm/dlmmaster.c
--- a/fs/ocfs2/dlm/dlmmaster.c~ocfs2-dlm-fix-race-between-purge-and-get-lock-resource
+++ a/fs/ocfs2/dlm/dlmmaster.c
@@ -757,6 +757,19 @@ 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);
_
--
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