Subject: Re: [Patch net-next] net_sched: avoid calling tcf_unbind_filter() in call_rcu callback

From: John Fastabend <[email-masked]>
Date: Tue, 30 Sep 2014 18:18:49 -0700

On 09/30/2014 05:53 PM, John Fastabend wrote:
> On 09/30/2014 04:07 PM, Cong Wang wrote:
>> This fixes the following crash:
>>
>> [   63.976822] general protection fault: 0000 [#1] PREEMPT SMP
>> DEBUG_PAGEALLOC
>> [   63.980094] CPU: 1 PID: 15 Comm: ksoftirqd/1 Not tainted
>> 3.17.0-rc6+ #648
>> [   63.980094] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
>> [   63.980094] task: ffff880117dea690 ti: ffff880117dfc000 task.ti:
>> ffff880117dfc000
>> [   63.980094] RIP: 0010:[<ffffffff817e6d07>]  [<ffffffff817e6d07>]
>> u32_destroy_key+0x27/0x6d
>> [   63.980094] RSP: 0018:ffff880117dffcc0  EFLAGS: 00010202
>> [   63.980094] RAX: ffff880117dea690 RBX: ffff8800d02e0820 RCX:
>> 0000000000000000
>> [   63.980094] RDX: 0000000000000001 RSI: 0000000000000002 RDI:
>> 6b6b6b6b6b6b6b6b
>> [   63.980094] RBP: ffff880117dffcd0 R08: 0000000000000000 R09:
>> 0000000000000000
>> [   63.980094] R10: 00006c0900006ba8 R11: 00006ba100006b9d R12:
>> 0000000000000001
>> [   63.980094] R13: ffff8800d02e0898 R14: ffffffff817e6d4d R15:
>> ffff880117387a30
>> [   63.980094] FS:  0000000000000000(0000) GS:ffff88011a800000(0000)
>> knlGS:0000000000000000
>> [   63.980094] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [   63.980094] CR2: 00007f07e6732fed CR3: 000000011665b000 CR4:
>> 00000000000006e0
>> [   63.980094] Stack:
>> [   63.980094]  ffff88011a9cd300 ffffffff82051ac0 ffff880117dffce0
>> ffffffff817e6d68
>> [   63.980094]  ffff880117dffd70 ffffffff810cb4c7 ffffffff810cb3cd
>> ffff880117dfffd8
>> [   63.980094]  ffff880117dea690 ffff880117dea690 ffff880117dfffd8
>> 000000000000000a
>> [   63.980094] Call Trace:
>> [   63.980094]  [<ffffffff817e6d68>] u32_delete_key_freepf_rcu+0x1b/0x1d
>> [   63.980094]  [<ffffffff810cb4c7>] rcu_process_callbacks+0x3bb/0x691
>> [   63.980094]  [<ffffffff810cb3cd>] ? rcu_process_callbacks+0x2c1/0x691
>> [   63.980094]  [<ffffffff817e6d4d>] ? u32_destroy_key+0x6d/0x6d
>> [   63.980094]  [<ffffffff810780a4>] __do_softirq+0x142/0x323
>> [   63.980094]  [<ffffffff810782a8>] run_ksoftirqd+0x23/0x53
>> [   63.980094]  [<ffffffff81092126>] smpboot_thread_fn+0x203/0x221
>> [   63.980094]  [<ffffffff81091f23>] ? smpboot_unpark_thread+0x33/0x33
>> [   63.980094]  [<ffffffff8108e44d>] kthread+0xc9/0xd1
>> [   63.980094]  [<ffffffff819e00ea>] ? do_wait_for_common+0xf8/0x125
>> [   63.980094]  [<ffffffff8108e384>] ? __kthread_parkme+0x61/0x61
>> [   63.980094]  [<ffffffff819e43ec>] ret_from_fork+0x7c/0xb0
>> [   63.980094]  [<ffffffff8108e384>] ? __kthread_parkme+0x61/0x61
>>
>> tp could be freed in call_rcu callback too, the order is not guaranteed.
>>
>> Cc: John Fastabend <[email-masked]>
>> Signed-off-by: Cong Wang <[email-masked]>
>> ---
>
> Thanks for catching this. What if we just drop tcf_exts_result
> I can't see how its being used anymore. It appears to just be passed
> around the ./net/sched files for some historic reason that is lost on
> me. Would you mind testing a patch if I sent it out?
>
> Maybe Jamal can shed some light?
>

Sorry I should say its not needed to pass to the actions,
tcf_exts_exec(). It _is_ needed here to get the class setup
correct. And the tcf_exts_exec() stuff is a separate patch.

Thanks again.

Acked-by: John Fastabend <[email-masked]>

>
>>   include/net/pkt_cls.h |  6 +-----
>>   net/sched/cls_u32.c   | 10 ++++++----
>>   2 files changed, 7 insertions(+), 9 deletions(-)
>>
>> diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
>> index 73f9532..ef44ad9 100644
>> --- a/include/net/pkt_cls.h
>> +++ b/include/net/pkt_cls.h
>> @@ -20,11 +20,7 @@ int unregister_tcf_proto_ops(struct tcf_proto_ops
>> *ops);
>>   static inline unsigned long
>>   __cls_set_class(unsigned long *clp, unsigned long cl)
>>   {
>> -    unsigned long old_cl;
>> -
>> -    old_cl = *clp;
>> -    *clp = cl;
>> -    return old_cl;
>> +    return xchg(clp, cl);
>>   }
>>
>>   static inline unsigned long
>> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
>> index 4be3ebf..0472909 100644
>> --- a/net/sched/cls_u32.c
>> +++ b/net/sched/cls_u32.c
>> @@ -358,7 +358,6 @@ static int u32_destroy_key(struct tcf_proto *tp,
>>                  struct tc_u_knode *n,
>>                  bool free_pf)
>>   {
>> -    tcf_unbind_filter(tp, &n->res);
>>       tcf_exts_destroy(&n->exts);
>>       if (n->ht_down)
>>           n->ht_down->refcnt--;
>> @@ -416,6 +415,7 @@ static int u32_delete_key(struct tcf_proto *tp,
>> struct tc_u_knode *key)
>>               if (pkp == key) {
>>                   RCU_INIT_POINTER(*kp, key->next);
>>
>> +                tcf_unbind_filter(tp, &key->res);
>>                   call_rcu(&key->rcu, u32_delete_key_freepf_rcu);
>>                   return 0;
>>               }
>> @@ -425,7 +425,7 @@ static int u32_delete_key(struct tcf_proto *tp,
>> struct tc_u_knode *key)
>>       return 0;
>>   }
>>
>> -static void u32_clear_hnode(struct tc_u_hnode *ht)
>> +static void u32_clear_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht)
>>   {
>>       struct tc_u_knode *n;
>>       unsigned int h;
>> @@ -434,6 +434,7 @@ static void u32_clear_hnode(struct tc_u_hnode *ht)
>>           while ((n = rtnl_dereference(ht->ht[h])) != NULL) {
>>               RCU_INIT_POINTER(ht->ht[h],
>>                        rtnl_dereference(n->next));
>> +            tcf_unbind_filter(tp, &n->res);
>>               call_rcu(&n->rcu, u32_delete_key_freepf_rcu);
>>           }
>>       }
>> @@ -447,7 +448,7 @@ static int u32_destroy_hnode(struct tcf_proto *tp,
>> struct tc_u_hnode *ht)
>>
>>       WARN_ON(ht->refcnt);
>>
>> -    u32_clear_hnode(ht);
>> +    u32_clear_hnode(tp, ht);
>>
>>       hn = &tp_c->hlist;
>>       for (phn = rtnl_dereference(*hn);
>> @@ -482,7 +483,7 @@ static void u32_destroy(struct tcf_proto *tp)
>>                ht;
>>                ht = rtnl_dereference(ht->next)) {
>>               ht->refcnt--;
>> -            u32_clear_hnode(ht);
>> +            u32_clear_hnode(tp, ht);
>>           }
>>
>>           while ((ht = rtnl_dereference(tp_c->hlist)) != NULL) {
>> @@ -731,6 +732,7 @@ static int u32_change(struct net *net, struct
>> sk_buff *in_skb,
>>           }
>>
>>           u32_replace_knode(tp, tp_c, new);
>> +        tcf_unbind_filter(tp, &n->res);
>>           call_rcu(&n->rcu, u32_delete_key_rcu);
>>           return 0;
>>       }
>>
>
>

-- 
John Fastabend         Intel Corporation