netdev - Re: Race condition in route lookup

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Message-ID: <52b3de47-d7f9-8ea9-10b1-0f7c11a2b31f@gmail.com>
Date:   Fri, 11 Oct 2019 15:27:41 -0600
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...sch.org>, Wei Wang <weiwan@...gle.com>,
        jesse@...ki-mvuki.org
Cc:     Martin KaFai Lau <kafai@...com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Race condition in route lookup

On 10/11/19 12:52 PM, Ido Schimmel wrote:
> On Fri, Oct 11, 2019 at 11:47:12AM -0700, Wei Wang wrote:
>> On Fri, Oct 11, 2019 at 11:25 AM Ido Schimmel <idosch@...sch.org> wrote:
>>>
>>> On Fri, Oct 11, 2019 at 09:17:42PM +0300, Ido Schimmel wrote:
>>>> On Fri, Oct 11, 2019 at 10:54:13AM -0700, Wei Wang wrote:
>>>>> On Fri, Oct 11, 2019 at 8:42 AM Ido Schimmel <idosch@...sch.org> wrote:
>>>>>>
>>>>>> On Fri, Oct 11, 2019 at 09:36:51AM -0500, Jesse Hathaway wrote:
>>>>>>> On Thu, Oct 10, 2019 at 3:31 AM Ido Schimmel <idosch@...sch.org> wrote:
>>>>>>>> I think it's working as expected. Here is my theory:
>>>>>>>>
>>>>>>>> If CPU0 is executing both the route get request and forwarding packets
>>>>>>>> through the directly connected interface, then the following can happen:
>>>>>>>>
>>>>>>>> <CPU0, t0> - In process context, per-CPU dst entry cached in the nexthop
>>>>>>>> is found. Not yet dumped to user space
>>>>>>>>
>>>>>>>> <Any CPU, t1> - Routes are added / removed, therefore invalidating the
>>>>>>>> cache by bumping 'net->ipv4.rt_genid'

IPv4 needs a change similar to what was done for IPv6 - only invalidate
dst's for the branches / table affected and not all dst's across the
namespace.