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From:   Thomas Gleixner <tglx@linutronix.de>
To:     paulmck@kernel.org,
        "Joel Fernandes \(Google\)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>, frextrite@gmail.com,
        Ingo Molnar <mingo@redhat.com>,
        Josh Triplett <josh@joshtriplett.org>, kernel-team@android.com,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        madhuparnabhowmik04@gmail.com,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        peterz@infradead.org, Petr Mladek <pmladek@suse.com>,
        rcu@vger.kernel.org, rostedt@goodmis.org, vpillai@digitalocean.com
Subject: Re: [PATCH v3 0/5] RCU dyntick nesting counter cleanups for rcu -dev
In-Reply-To: <20200516171223.GC2639@paulmck-ThinkPad-P72>
References: <20200504120505.89351-1-joel@joelfernandes.org> <20200504171532.GR2869@paulmck-ThinkPad-P72> <20200504174413.GA8883@paulmck-ThinkPad-P72> <20200516171223.GC2639@paulmck-ThinkPad-P72>
Date:   Sun, 17 May 2020 12:26:43 +0200
Message-ID: <87wo5adfh8.fsf@nanos.tec.linutronix.de>
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Paul,

"Paul E. McKenney" <paulmck@kernel.org> writes:
> And I have allegedly resolved the conflicts with Thomas's and Peter's
> series, or at least the noinstr-rcu-nmi-2020-05-15 branch of that series.
> At least one conflict was completely invisible to "git rebase" (but
> fortunately blindingly obvious to the compiler).  This naturally makes
> me suspect that additional adjustments might be needed.  Especially
> given that misplaced instrumentation_begin() and instrumentation_end()
> calls are invisible not only to the compiler, but also to rcutorture in
> my setup.  (For example, tracing before instrumentation_begin() or after
> instrumentation_end() is a bug.)

there is tooling to verify that. If you merge

  git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git entry-v7-full

into your dev branch (trivial conflict) and after building it, run:

 objtool check -fal $BUILDIR/vmlinux.o

Note: This only covers built-in code. So if you have code you want to
check make sure it's not built as module.

Just did that and it complains about:

../build/vmlinux.o: warning: objtool: rcu_eqs_enter.constprop.0()+0xa9: call to rcu_preempt_deferred_qs() leaves .noinstr.text section

But that's even the case on my branch without your changes.

The call to rcu_preempt_deferred_qs() is definitely before
instrumentation_end() so this needs to be investigated on the objtool
side. Peter?

Thanks,

        tglx