netdev - Re: BUG: using __this_cpu_add() in preemptible in tcp_make

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Message-ID: <8cd33923-a21d-397c-e46b-2a068c287b03@cloudflare.com>
Date:   Wed, 18 Jan 2023 14:27:17 -0600
From:   Frederick Lawler <fred@...udflare.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     netdev@...r.kernel.org, kernel-team@...udflare.com,
        davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        kuba@...nel.org, pabeni@...hat.com
Subject: Re: BUG: using __this_cpu_add() in preemptible in tcp_make_synack()

Hi Eric,

On 1/18/23 11:07 AM, Eric Dumazet wrote:
>>
>> Thanks,
>> Fred
> 
> Thanks for the report
> 
> I guess this part has been missed in commit 0a375c822497ed6a
> 
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 71d01cf3c13eb4bd3d314ef140568d2ffd6a499e..ba839e441450f195012a8d77cb9e5ed956962d2f
> 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3605,7 +3605,7 @@ struct sk_buff *tcp_make_synack(const struct
> sock *sk, struct dst_entry *dst,
>          th->window = htons(min(req->rsk_rcv_wnd, 65535U));
>          tcp_options_write(th, NULL, &opts);
>          th->doff = (tcp_header_size >> 2);
> -       __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
> +       TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
> 
>   #ifdef CONFIG_TCP_MD5SIG
>          /* Okay, we have all we need - do the md5 hash if needed */

Thanks for the fast response!

I applied this change to our Kernel and started the rollout process. 
I'll report back with any findings once we have sufficient data.