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

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Message-ID: <CANn89iLMUP8_HnmmstGHxh7iR+EqPdEAUNM7OfyDdHJFNdBu3g@mail.gmail.com>
Date:   Mon, 23 Jan 2023 16:49:37 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Frederick Lawler <fred@...udflare.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()

On Mon, Jan 23, 2023 at 4:46 PM Frederick Lawler <fred@...udflare.com> wrote:
>
> Hi Eric,
>
> On 1/18/23 11:07 AM, Eric Dumazet wrote:
> > On Wed, Jan 18, 2023 at 5:56 PM Frederick Lawler <fred@...udflare.com> wrote:
> >>
> >> Hello,
> >>
> >> We've been testing Linux 6.1.4, and came across an intermittent "BUG:
> >> using __this_cpu_add() in preemptible" [1] in our services leveraging
> >> TCP_FASTOPEN and our kernel configured with:
> >>
> >> [snip]
> >
> > 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 */
>
>
> Tested-by: Frederick Lawler <fred@...udflare.com>

Thanks for testing, I will submit the fix today.