linux-kernel - Re: [4.4-rt PATCH] trace: use rcuidle version for preemptoff

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Date:	Fri, 26 Feb 2016 11:25:13 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	rostedt@...dmis.org
Cc:	tglx@...utronix.de, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Yang Shi <yang.shi@...driver.com>
Subject: Re: [4.4-rt PATCH] trace: use rcuidle version for preemptoff_hist
 trace point

Steven, does this change look reasonable to you? I remember we had a
discussion about this.

* Yang Shi | 2016-02-23 13:23:23 [-0800]:

>When running -rt kernel with both PREEMPT_OFF_HIST and LOCKDEP enabled,
>the below error is reported:
>
> [ INFO: suspicious RCU usage. ]
> 4.4.1-rt6 #1 Not tainted
> include/trace/events/hist.h:31 suspicious rcu_dereference_check() usage!
>
> other info that might help us debug this:
>
> RCU used illegally from idle CPU!
> rcu_scheduler_active = 1, debug_locks = 0
> RCU used illegally from extended quiescent state!
> no locks held by swapper/0/0.
>
> stack backtrace:
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.1-rt6-WR8.0.0.0_standard #1
> Stack : 0000000000000006 0000000000000000 ffffffff81ca8c38 ffffffff81c8fc80
>    ffffffff811bdd68 ffffffff81cb0000 0000000000000000 ffffffff81cb0000
>    0000000000000000 0000000000000000 0000000000000004 0000000000000000
>    0000000000000004 ffffffff811bdf50 0000000000000000 ffffffff82b60000
>    0000000000000000 ffffffff812897ac ffffffff819f0000 000000000000000b
>    ffffffff811be460 ffffffff81b7c588 ffffffff81c8fc80 0000000000000000
>    0000000000000000 ffffffff81ec7f88 ffffffff81d70000 ffffffff81b70000
>    ffffffff81c90000 ffffffff81c3fb00 ffffffff81c3fc28 ffffffff815e6f98
>    0000000000000000 ffffffff81c8fa87 ffffffff81b70958 ffffffff811bf2c4
>    0707fe32e8d60ca5 ffffffff81126d60 0000000000000000 0000000000000000
>    ...
> Call Trace:
> [<ffffffff81126d60>] show_stack+0xe8/0x108
> [<ffffffff815e6f98>] dump_stack+0x88/0xb0
> [<ffffffff8124b88c>] time_hardirqs_off+0x204/0x300
> [<ffffffff811aa5dc>] trace_hardirqs_off_caller+0x24/0xe8
> [<ffffffff811a4ec4>] cpu_startup_entry+0x39c/0x508
> [<ffffffff81d7dc68>] start_kernel+0x584/0x5a0
>
>Replace regular trace_preemptoff_hist to rcuidle version to avoid the error.
>
>Signed-off-by: Yang Shi <yang.shi@...driver.com>
>---
>I recall the rcuidle version is used by 4.1-rt, but not sure why it is dropped
>in 4.4-rt. It looks such fix is still needed. 
>
> kernel/trace/trace_irqsoff.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
>diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
>index 36e584f..069942c 100644
>--- a/kernel/trace/trace_irqsoff.c
>+++ b/kernel/trace/trace_irqsoff.c
>@@ -421,13 +421,13 @@ void start_critical_timings(void)
> {
> 	if (preempt_trace() || irq_trace())
> 		start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
>-	trace_preemptirqsoff_hist(TRACE_START, 1);
>+	trace_preemptirqsoff_hist_rcuidle(TRACE_START, 1);
> }
> EXPORT_SYMBOL_GPL(start_critical_timings);
> 
> void stop_critical_timings(void)
> {
>-	trace_preemptirqsoff_hist(TRACE_STOP, 0);
>+	trace_preemptirqsoff_hist_rcuidle(TRACE_STOP, 0);
> 	if (preempt_trace() || irq_trace())
> 		stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
> }
>@@ -437,7 +437,7 @@ EXPORT_SYMBOL_GPL(stop_critical_timings);
> #ifdef CONFIG_PROVE_LOCKING
> void time_hardirqs_on(unsigned long a0, unsigned long a1)
> {
>-	trace_preemptirqsoff_hist(IRQS_ON, 0);
>+	trace_preemptirqsoff_hist_rcuidle(IRQS_ON, 0);
> 	if (!preempt_trace() && irq_trace())
> 		stop_critical_timing(a0, a1);
> }
>@@ -446,7 +446,7 @@ void time_hardirqs_off(unsigned long a0, unsigned long a1)
> {
> 	if (!preempt_trace() && irq_trace())
> 		start_critical_timing(a0, a1);
>-	trace_preemptirqsoff_hist(IRQS_OFF, 1);
>+	trace_preemptirqsoff_hist_rcuidle(IRQS_OFF, 1);
> }
> 
> #else /* !CONFIG_PROVE_LOCKING */
>-- 
>2.0.2
>
>--
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