Re: [PATCH net v4] tcp: warn on bogus MSS and try to amend it

[David Miller <davem@davemloft.net>]

From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: Mon,  5 Dec 2016 18:37:13 -0200

> There have been some reports lately about TCP connection stalls caused
> by NIC drivers that aren't setting gso_size on aggregated packets on rx
> path. This causes TCP to assume that the MSS is actually the size of the
> aggregated packet, which is invalid.
> 
> Although the proper fix is to be done at each driver, it's often hard
> and cumbersome for one to debug, come to such root cause and report/fix
> it.
> 
> This patch amends this situation in two ways. First, it adds a warning
> on when this situation occurs, so it gives a hint to those trying to
> debug this. It also limit the maximum probed MSS to the adverised MSS,
> as it should never be any higher than that.
> 
> The result is that the connection may not have the best performance ever
> but it shouldn't stall, and the admin will have a hint on what to look
> for.
> 
> Tested with virtio by forcing gso_size to 0.
> 
> v2: updated msg per David's suggestion
> v3: use skb_iif to find the interface and also log its name, per Eric
>     Dumazet's suggestion. As the skb may be backlogged and the interface
>     gone by then, we need to check if the number still has a meaning.
> v4: use helper tcp_gro_dev_warn() and avoid pr_warn_once inside __once, per
>     David's suggestion
> 
> Cc: Jonathan Maxwell <jmaxwell37@gmail.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Applied, thanks Marcelo.