Re: [PATCH nf] netfilter: fix using __this_cpu_add in preemptible in nf_flow_table_offload

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Thu, Nov 24, 2022 at 12:54:10PM -0500, Xin Long wrote:
> flow_offload_queue_work() can be called in workqueue without
> bh disabled, like the call trace showed in my act_ct testing,
> calling NF_FLOW_TABLE_STAT_INC() there would cause a call
> trace:
> 
>   BUG: using __this_cpu_add() in preemptible [00000000] code: kworker/u4:0/138560
>   caller is flow_offload_queue_work+0xec/0x1b0 [nf_flow_table]
>   Workqueue: act_ct_workqueue tcf_ct_flow_table_cleanup_work [act_ct]
>   Call Trace:
>    <TASK>
>    dump_stack_lvl+0x33/0x46
>    check_preemption_disabled+0xc3/0xf0
>    flow_offload_queue_work+0xec/0x1b0 [nf_flow_table]
>    nf_flow_table_iterate+0x138/0x170 [nf_flow_table]
>    nf_flow_table_free+0x140/0x1a0 [nf_flow_table]
>    tcf_ct_flow_table_cleanup_work+0x2f/0x2b0 [act_ct]
>    process_one_work+0x6a3/0x1030
>    worker_thread+0x8a/0xdf0
> 
> This patch fixes it by using NF_FLOW_TABLE_STAT_INC_ATOMIC()
> instead in flow_offload_queue_work().
> 
> Note that for FLOW_CLS_REPLACE branch in flow_offload_queue_work(),
> it may not be called in preemptible path, but it's good to use
> NF_FLOW_TABLE_STAT_INC_ATOMIC() for all cases in
> flow_offload_queue_work().

Applied, thanks