linux-kernel - Re: [PATCH -rcu/kcsan 23/23] objtool, kcsan: Remove memory barrier instrumentation from noinstr

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Message-ID: <YVxjH2AtjvB8BDMD@hirez.programming.kicks-ass.net>
Date:   Tue, 5 Oct 2021 16:37:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH -rcu/kcsan 23/23] objtool, kcsan: Remove memory barrier
 instrumentation from noinstr

On Tue, Oct 05, 2021 at 12:59:05PM +0200, Marco Elver wrote:
> Teach objtool to turn instrumentation required for memory barrier
> modeling into nops in noinstr text.
> 
> The __tsan_func_entry/exit calls are still emitted by compilers even
> with the __no_sanitize_thread attribute. The memory barrier
> instrumentation will be inserted explicitly (without compiler help), and
> thus needs to also explicitly be removed.

How is arm64 and others using kernel/entry + noinstr going to fix this?

ISTR they fully rely on the compilers not emitting instrumentation,
since they don't have objtool to fix up stray issues like this.