[Ocfs2-devel] [PATCH] ocfs2: fix a potential deadlock in dlm_reset_mleres_owner()

[alex chen]

In dlm_reset_mleres_owner(), we will lock
dlm_lock_resource->spinlock after locking dlm_ctxt->master_lock,
which breaks the spinlock lock ordering:
 dlm_domain_lock
 struct dlm_ctxt->spinlock
 struct dlm_lock_resource->spinlock
 struct dlm_ctxt->master_lock

Fix it by unlocking dlm_ctxt->master_lock before locking
dlm_lock_resource->spinlock and restarting to clean master list.

Signed-off-by: Alex Chen <alex.chen at huawei.com>
Reviewed-by: Jun Piao <piaojun at huawei.com>
---
 fs/ocfs2/dlm/dlmmaster.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 3e04279..0df939a 100644
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -3287,14 +3287,23 @@ static struct dlm_lock_resource *dlm_reset_mleres_owner(struct dlm_ctxt *dlm,
 {
 	struct dlm_lock_resource *res;

+	assert_spin_locked(&dlm->spinlock);
+	assert_spin_locked(&dlm->master_lock);
+
 	/* Find the lockres associated to the mle and set its owner to UNK */
-	res = __dlm_lookup_lockres(dlm, mle->mname, mle->mnamelen,
+	res = __dlm_lookup_lockres_full(dlm, mle->mname, mle->mnamelen,
 				   mle->mnamehash);
 	if (res) {
 		spin_unlock(&dlm->master_lock);

-		/* move lockres onto recovery list */
 		spin_lock(&res->spinlock);
+		if (res->state & DLM_LOCK_RES_DROPPING_REF) {
+			spin_unlock(&res->spinlock);
+			dlm_lockres_put(res);
+			return NULL;
+		}
+
+		/* move lockres onto recovery list */
 		dlm_set_lockres_owner(dlm, res, DLM_LOCK_RES_OWNER_UNKNOWN);
 		dlm_move_lockres_to_recovery_list(dlm, res);
 		spin_unlock(&res->spinlock);
-- 
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