netdev - Re: Race condition in route lookup

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Message-ID: <CANSNSoVMXcPpnHBYvDJ9P4PVB2pLGEBHW2j-iD7QqQrFmGFt_Q@mail.gmail.com>
Date:   Tue, 15 Oct 2019 09:29:44 -0500
From:   Jesse Hathaway <jesse@...ki-mvuki.org>
To:     Wei Wang <weiwan@...gle.com>
Cc:     Ido Schimmel <idosch@...sch.org>, Martin KaFai Lau <kafai@...com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Race condition in route lookup

On Fri, Oct 11, 2019 at 12:54 PM Wei Wang <weiwan@...gle.com> wrote:
> Hmm... Yes... I would think a per-CPU input cache should work for the
> case above.
> Another idea is: instead of calling dst_dev_put() in rt_cache_route()
> to switch out the dev, we call, rt_add_uncached_list() to add this
> obsolete dst cache to the uncached list. And if the device gets
> unregistered, rt_flush_dev() takes care of all dst entries in the
> uncached list. I think that would work too.
>
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index dc1f510a7c81..ee618d4234ce 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -1482,7 +1482,7 @@ static bool rt_cache_route(struct fib_nh_common
> *nhc, struct rtable *rt)
>         prev = cmpxchg(p, orig, rt);
>         if (prev == orig) {
>                 if (orig) {
> -                       dst_dev_put(&orig->dst);
> +                       rt_add_uncached_list(orig);
>                         dst_release(&orig->dst);
>                 }
>         } else {
>

Thanks Wei for your work on this issue,

Any chance this patch will make it into 5.4?