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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 5 Oct 2021 12:46:43 -0700
Message-ID: <CAHk-=wiL+wyCOTedh48Oz0cNOKJq2GNwtxg6423hf-1FuGrv_A@mail.gmail.com>
Subject: Re: [RFC][PATCH] rcu: Use typeof(p) instead of typeof(*p) *
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Jan Engelhardt <jengelh@inai.de>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Paul <paulmck@linux.vnet.ibm.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        "Joel Fernandes, Google" <joel@joelfernandes.org>,
        Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        "David S. Miller" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>, rcu <rcu@vger.kernel.org>,
        netfilter-devel <netfilter-devel@vger.kernel.org>,
        coreteam <coreteam@netfilter.org>,
        netdev <netdev@vger.kernel.org>
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On Tue, Oct 5, 2021 at 12:40 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> I may try it, because exposing the structure I want to hide, is pulling out
> a lot of other crap with it :-p

One option is just "don't do rcu_access of a pointer that you're not
supposed to touch in a file that isn't supposed to touch it".

IOW, why are you doing that

     pid_list = rcu_dereference_sched(tr->function_pids);

in a place that isn't supposed to look at the pid_list in the first place?

Yeah, yeah, I see how you just pass it to trace_ignore_this_task() as
an argument, but maybe the real fix is to just pass that trace_array
pointer instead?

IOW, if you want to keep that structure private, maybe you really just
shouldn't have non-private users of it randomly doing RCU lookups of
it?

                  Linus