From: Junxiao Bi <[email protected]>
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 <[email protected]>
Cc: Joseph Qi <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
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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