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Date:   Fri, 1 Apr 2022 21:31:59 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Vasily Averin <vasily.averin@linux.dev>
Cc:     Florian Westphal <fw@strlen.de>,
        Pablo Neira Ayuso <pablo@netfilter.org>, kernel@openvz.org,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        netfilter-devel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Roman Gushchin <roman.gushchin@linux.dev>
Subject: Re: [PATCH nft] nft: memcg accounting for dynamically allocated
 objects
Message-ID: <20220401193159.GB28321@breakpoint.cc>
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Vasily Averin <vasily.averin@linux.dev> wrote:
> > Same problem as connlimit, can be called from packet path.
> > Basically all GFP_ATOMIC are suspicious.
> > 
> > Not sure how to resolve this, similar mechanics in iptables world (e.g.
> > connlimit or SET target) don't use memcg accounting.
> > 
> > Perhaps for now resend with only the GFP_KERNEL parts converted?
> > Those are safe.
> 
> It is safe for packet path too, _ACCOUNT allocation will not be able to find memcg
> in case of "!in_task()" context.
> On the other hand any additional checks on such path will affect performance.

I'm not sure this works with ksoftirqd serving network stack?

> Could you please estimate how often is this code used in the case of nft vs packet path?

It depends on user configuration.
Update from packet path is used for things like port knocking or other
dyanamic filter lists, or somehing like Limiting connections to x-per-address/subnet and so on.

> If the opposite is the case, then I can add __GFP_ACCOUNT flag depending on in_task() check.

But what task/memcg is used for the accounting in that case?