linux-kernel - Re: [PATCH 3/3] netfilter: x_tables: Use correct memory barriers.

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Message-ID: <631d774f41a564b28d40a5639a58f1ab0d7f6e03.camel@alliedtelesis.co.nz>
Date:   Fri, 5 Mar 2021 03:30:30 +0000
From:   Mark Tomlinson <Mark.Tomlinson@...iedtelesis.co.nz>
To:     "fw@...len.de" <fw@...len.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pablo@...filter.org" <pablo@...filter.org>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
        "kadlec@...filter.org" <kadlec@...filter.org>
Subject: Re: [PATCH 3/3] netfilter: x_tables: Use correct memory barriers.

On Thu, 2021-03-04 at 08:46 +0100, Florian Westphal wrote:
> Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz> wrote:
> > Changing to using smp_mb() instead of smp_wmb() fixes the kernel panic
> > reported in cc00bcaa5899,
> 
> Can you reproduce the crashes without this change?

Yes. In our test environment we were seeing a kernel panic approx. twice
a day, with a similar output to that shown in Subash's patch (cc00bcaa5899).
With this patch we are not seeing any issue. The CPU is a dual-core ARM
Cortex-A9.

> > How much of an impact is the MB change on the packet path?

I will run our throughput tests and get these results.

I have a script which makes around 200 calls to iptables. This was taking
11.59s and now is back to 1.16s.