net/sched: cls_api: Fix lockup on flushing explicitly created chain

[ Upstream commit c9a82bec02c339cdda99b37c5e62b3b71fc4209c ]

Mingshuai Ren reports:

When a new chain is added by using tc, one soft lockup alarm will be
 generated after delete the prio 0 filter of the chain. To reproduce
 the problem, perform the following steps:
(1) tc qdisc add dev eth0 root handle 1: htb default 1
(2) tc chain add dev eth0
(3) tc filter del dev eth0 chain 0 parent 1: prio 0
(4) tc filter add dev eth0 chain 0 parent 1:

Fix the issue by accounting for additional reference to chains that are
explicitly created by RTM_NEWCHAIN message as opposed to implicitly by
RTM_NEWTFILTER message.

Fixes: 726d061286ce ("net: sched: prevent insertion of new classifiers during chain flush")
Reported-by: Mingshuai Ren <renmingshuai@huawei.com>
Closes: https://lore.kernel.org/lkml/87legswvi3.fsf@nvidia.com/T/
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Link: https://lore.kernel.org/r/20230612093426.2867183-1-vladbu@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 0dbfc37..445ab1b 100644 (file)
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -552,8 +552,8 @@ static void __tcf_chain_put(struct tcf_chain *chain, bool by_act,
 {
        struct tcf_block *block = chain->block;
        const struct tcf_proto_ops *tmplt_ops;
+       unsigned int refcnt, non_act_refcnt;
        bool free_block = false;
-       unsigned int refcnt;
        void *tmplt_priv;
 
        mutex_lock(&block->lock);
@@ -573,13 +573,15 @@ static void __tcf_chain_put(struct tcf_chain *chain, bool by_act,
         * save these to temporary variables.
         */
        refcnt = --chain->refcnt;
+       non_act_refcnt = refcnt - chain->action_refcnt;
        tmplt_ops = chain->tmplt_ops;
        tmplt_priv = chain->tmplt_priv;
 
-       /* The last dropped non-action reference will trigger notification. */
-       if (refcnt - chain->action_refcnt == 0 && !by_act) {
-               tc_chain_notify_delete(tmplt_ops, tmplt_priv, chain->index,
-                                      block, NULL, 0, 0, false);
+       if (non_act_refcnt == chain->explicitly_created && !by_act) {
+               if (non_act_refcnt == 0)
+                       tc_chain_notify_delete(tmplt_ops, tmplt_priv,
+                                              chain->index, block, NULL, 0, 0,
+                                              false);
                /* Last reference to chain, no need to lock. */
                chain->flushing = false;
        }