netdev - Re: [PATCH net-next] tcp: add accessors to read/set tp->snd

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Message-ID: <20220406122616.302dc84c@kernel.org>
Date:   Wed, 6 Apr 2022 12:26:16 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] tcp: add accessors to read/set tp->snd_cwnd

On Tue,  5 Apr 2022 16:35:38 -0700 Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> We had various bugs over the years with code
> breaking the assumption that tp->snd_cwnd is greater
> than zero.
> 
> Lately, syzbot reported the WARN_ON_ONCE(!tp->prior_cwnd) added
> in commit 8b8a321ff72c ("tcp: fix zero cwnd in tcp_cwnd_reduction")
> can trigger, and without a repro we would have to spend
> considerable time finding the bug.
> 
> Instead of complaining too late, we want to catch where
> and when tp->snd_cwnd is set to an illegal value.

I wish we could cover BPF CCs as well :)