netdev - Re: [PATCH net] netfilter: nf_tables: prefer kfree

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Message-ID: <CANn89iLz4yML_RktHUadAkU966h9QCRJQ=cMPVzUDU7dHXg0sw@mail.gmail.com>
Date:   Tue, 22 Feb 2022 12:07:05 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        netfilter-devel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] netfilter: nf_tables: prefer kfree_rcu(ptr, rcu) variant

On Tue, Feb 22, 2022 at 11:46 AM Florian Westphal <fw@...len.de> wrote:
>
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > While kfree_rcu(ptr) _is_ supported, it has some limitations.
> >
> > Given that 99.99% of kfree_rcu() users [1] use the legacy
> > two parameters variant, and @catchall objects do have an rcu head,
> > simply use it.
> >
> > Choice of kfree_rcu(ptr) variant was probably not intentional.
>
> In case someone wondered, this causes expensive
> sycnhronize_rcu + kfree for each removal operation.

This fallback to synchronize_rcu() only happens if kvfree_call_rcu() has been
unable to allocate a new block of memory.

But yes, I guess I would add a Fixes: tag, because we can easily avoid
this potential issue.

Pablo, if not too late:

Fixes: aaa31047a6d2 ("netfilter: nftables: add catch-all set element support")

>
> Reviewed-by: Florian Westphal <fw@...len.de>
>