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

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