[PATCH] net/sched: Set the flushing flags to false to prevent an infinite loop

[renmingshuai]

>On 06/06/2023 11:45, renmingshuai wrote:
>> 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:
>
>This seems like it could be added to tdc or 3 and 4 must be run in parallel?
3 and 4 do not need to be run inparallel. When a new chain is added by the
 way as step 1 and the step 3 is completed, this problem always occurs
 whenever step 4 is run.
>> 
>> 
>> The refcnt of the chain added by step 2 is equal to 1. After step 3,
>>   the flushing flag of the chain is set to true in the tcf_chain_flush()
>>   called by tc_del_tfilter() because the prio is 0. In this case, if
>>   we add a new filter to this chain, it will never succeed and try again
>>   and again because the refresh flash is always true and refcnt is 1.
>>   A soft lock alarm is generated 20 seconds later.
>> The stack is show as below:
>> 
>> Kernel panic - not syncing: softlockup: hung tasks
>> CPU: 2 PID: 3321861 Comm: tc Kdump: loaded Tainted: G
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
>> Call Trace:
>>   <IRQ>
>>   dump_stack+0x57/0x6e
>>   panic+0x196/0x3ec
>>   watchdog_timer_fn.cold+0x16/0x5c
>>   __run_hrtimer+0x5e/0x190
>>   __hrtimer_run_queues+0x8a/0xe0
>>   hrtimer_interrupt+0x110/0x2c0
>>   ? irqtime_account_irq+0x49/0xf0
>>   __sysvec_apic_timer_interrupt+0x5f/0xe0
>>   asm_call_irq_on_stack+0x12/0x20
>>   </IRQ>
>>   sysvec_apic_timer_interrupt+0x72/0x80
>>   asm_sysvec_apic_timer_interrupt+0x12/0x20
>> RIP: 0010:mutex_lock+0x24/0x70
>> RSP: 0018:ffffa836004ab9a8 EFLAGS: 00000246
>> RAX: 0000000000000000 RBX: ffff95bb02d76700 RCX: 0000000000000000
>> RDX: ffff95bb27462100 RSI: 0000000000000000 RDI: ffff95ba5b527000
>> RBP: ffff95ba5b527000 R08: 0000000000000001 R09: ffffa836004abbb8
>> R10: 000000000000000f R11: 0000000000000000 R12: 0000000000000000
>> R13: ffff95ba5b527000 R14: ffffa836004abbb8 R15: 0000000000000001
>>   __tcf_chain_put+0x27/0x200
>>   tc_new_tfilter+0x5e8/0x810
>>   ? tc_setup_cb_add+0x210/0x210
>>   rtnetlink_rcv_msg+0x2e3/0x380
>>   ? rtnl_calcit.isra.0+0x120/0x120
>>   netlink_rcv_skb+0x50/0x100
>>   netlink_unicast+0x12d/0x1d0
>>   netlink_sendmsg+0x286/0x490
>>   sock_sendmsg+0x62/0x70
>>   ____sys_sendmsg+0x24c/0x2c0
>>   ? import_iovec+0x17/0x20
>>   ? sendmsg_copy_msghdr+0x80/0xa0
>>   ___sys_sendmsg+0x75/0xc0
>>   ? do_fault_around+0x118/0x160
>>   ? do_read_fault+0x68/0xf0
>>   ? __handle_mm_fault+0x3f9/0x6f0
>>   __sys_sendmsg+0x59/0xa0
>>   do_syscall_64+0x33/0x40
>>   entry_SYSCALL_64_after_hwframe+0x61/0xc6
>> RIP: 0033:0x7f96705b8247
>> RSP: 002b:00007ffe552e9dc8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f96705b8247
>> RDX: 0000000000000000 RSI: 00007ffe552e9e40 RDI: 0000000000000003
>> RBP: 0000000000000001 R08: 0000000000000001 R09: 0000558113f678b0
>> R10: 00007f967069ab00 R11: 0000000000000246 R12: 00000000647ea089
>> R13: 00007ffe552e9f30 R14: 0000000000000001 R15: 0000558113175f00
>> 
>> To avoid this case, set chain->flushing to be false if the chain->refcnt
>>   is 1 after flushing the chain when prio is 0.
>> 
>> Fixes: 726d061286ce ("net: sched: prevent insertion of new classifiers during chain flush")
>> Signed-off-by: Ren Mingshuai <renmingshuai@xxxxxxxxxx>
>> ---
>>   net/sched/cls_api.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>> 
>> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>> index 2621550bfddc..68be55d75831 100644
>> --- a/net/sched/cls_api.c
>> +++ b/net/sched/cls_api.c
>> @@ -2442,6 +2442,13 @@ static int tc_del_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
>>   		tfilter_notify_chain(net, skb, block, q, parent, n,
>>   				     chain, RTM_DELTFILTER, extack);
>>   		tcf_chain_flush(chain, rtnl_held);
>> +		/* Set the flushing flags to false to prevent an infinite loop
>> +		 * when a new filter is added.
>> +		 */
>> +		mutex_lock(&chain->filter_chain_lock);
>> +		if (chain->refcnt == 1)
>> +			chain->flushing = false;
>> +		mutex_unlock(&chain->filter_chain_lock);
>>   		err = 0;
>>   		goto errout;
>>   	}