From: Junjie Cao <junjie.cao@intel.com>
To: Fernando Fernandez Mancera <fmancera@suse.de>
Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com,
kuba@kernel.org, pabeni@redhat.com, horms@kernel.org,
dsahern@kernel.org, idosch@nvidia.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next] net: dropreason: add SKB_DROP_REASON_IP_TTL_EXCEEDED
Date: Tue, 25 Aug 2026 20:13:30 +0800 [thread overview]
Message-ID: <20260825121330.338380-1-junjie.cao@intel.com> (raw)
In-Reply-To: <9abd7020-90b3-45e3-84ef-ca31b760feaf@suse.de>
On Tue, Aug 25, 2026 at 11:36 AM Fernando Fernandez Mancera
<fmancera@suse.de> wrote:
> The patch is sound but isn't this drop reason a bit redundant? I mean, a
> simple check on traffic should have shown to the user that TTL is been
> exceeded.
Checking traffic for TTL presumes TTL is already the suspect. The reason
string is what points the investigation: in the linked bug, IP_INHDR read
as a broken header and the capture time went to checksums -- RX offload,
tc csum actions, both libvirt firewall backends. Nobody filters on TTL
while the kernel is saying the header is bad.
dropwatch and perf report the reason without a capture; that only helps
if the string is precise. IPV6_NDISC_HOP_LIMIT and TCP_MINTTL are as
visible in a capture as this one, and both have their own reason.
The exthdrs.c hunks also cover three drops that report no reason at all.
> In any case, net-next is currently closed [1]. Please send this after it
> re-opens.
Will repost when it reopens.
prev parent reply other threads:[~2026-08-25 12:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-25 7:39 [PATCH net-next] net: dropreason: add SKB_DROP_REASON_IP_TTL_EXCEEDED Junjie Cao
2026-08-25 7:46 ` Eric Dumazet
2026-08-25 9:36 ` Fernando Fernandez Mancera
2026-08-25 12:13 ` Junjie Cao [this message]
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