Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage

From: Joel Fernandes <joelaf@google.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Joel Fernandes <joel@joelfernandes.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Cc: Android Kernel" <kernel-team@android.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Byungchul Park <byungchul.park@lge.com>,
	Ingo Molnar <mingo@redhat.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Glexiner <tglx@linutronix.de>,
	Tom Zanussi <tom.zanussi@linux.intel.com>
Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage
Date: Tue, 7 Aug 2018 19:13:32 -0700	[thread overview]
Message-ID: <CAJWu+opjqKgZj30PYpyvip=EtP8CuqaEy65++nuvj37QMT6GCw@mail.gmail.com> (raw)
In-Reply-To: <20180807215522.04114097@vmware.local.home>

On Tue, Aug 7, 2018 at 6:55 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Tue, 7 Aug 2018 18:17:42 -0700
> Joel Fernandes <joelaf@google.com> wrote:
>
>> From 6986af946ceb04fc9ddc6d5b45fc559b6807e465 Mon Sep 17 00:00:00 2001
>> From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
>> Date: Sun, 5 Aug 2018 20:17:41 -0700
>> Subject: [PATCH] tracepoint: Run tracepoints even after CPU is offline
>>
>> Commit f37755490fe9 ("tracepoints: Do not trace when cpu is offline")
>> causes a problem for lockdep using tracepoint code. Once a CPU is
>> offline, tracepoints donot get called, however this causes a big problem
>> for lockdep probes that need to run so that IRQ annotations are marked
>> correctly.
>>
>> A race is possible where while the CPU is going offline, an interrupt
>> can come in and then a lockdep assert causes an annotation warning:
>>
>> [  106.551354] IRQs not enabled as expected
>> [  106.551785] WARNING: CPU: 1 PID: 0 at kernel/time/tick-sched.c:982
>>                                          tick_nohz_idle_enter+0x99/0xb0
>> [  106.552964] Modules linked in:
>> [  106.553299] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G        W
>>
>> We need tracepoints to run as late as possible. This commit fixes the
>> issue by removing the cpu_online check in tracepoint code that was
>> introduced in the mentioned commit, however we now switch to using SRCU
>> for all tracepoints and special handle calling tracepoints from NMI so
>> that we don't run into issues that result from using sched-RCU when the
>> CPUs are marked to be offline.
>>
>> Fixes: c3bc8fd637a9 ("tracing: Centralize preemptirq tracepoints and
>>                       unify their usage")
>> Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>
>
> The above change log doesn't look like it matches the NMI patch.
>
> Can you resend with just the NMI changes? I already handled the cpu
> offline ones.

Ok, sent with "cpu offline" changes dropped, here it is:
https://lore.kernel.org/patchwork/patch/972657/

If you could add your Reported-by to it, that would be great as well.

>
> But I may still have concerns with this patch.

Ok let me know what you think.

Thanks!

 - Joel