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Date:   Wed, 6 Jul 2022 18:54:17 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: rawip: delayed and mis-sequenced transmits
Message-ID: <20220706185417.2fcbcdf0@kernel.org>
In-Reply-To: <433be56da42f4ab2b7722c1caed3a747@AcuMS.aculab.com>
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On Wed, 6 Jul 2022 15:54:18 +0000 David Laight wrote:
> Anyone any ideas before I start digging through the kernel code?

If the qdisc is pfifo_fast and kernel is old there could be races.
But I don't think that's likely given you probably run something
recent and next packet tx would usually flush the stuck packet.
In any case - switching qdisc could be a useful test, also bpftrace 
is your friend for catching patckets with long sojourn time.