linux-kernel - [PATCH] trace: irqsoff: Fix function tracing in preempt and preemptirqsoff tracers

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Message-Id: <1457770023-88559-1-git-send-email-agnel.joel@gmail.com>
Date:	Sat, 12 Mar 2016 00:07:03 -0800
From:	Joel Fernandes <agnel.joel@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] trace: irqsoff: Fix function tracing in preempt and preemptirqsoff tracers

All functions aren't traced in critical sections where preemption is disabled
and interrupts are enabled in preempt* tracers because current behavior is to
check if interrupts are disabled and if they are not, then we don't trace these
functions. So here we do the correct checks depending on tracer type and allow
these functions to be traced.

One example is when interrupts are enabled before softirq processing, with the
patch, these functions are traced as well.

   <...>-2265    1d.h1 3419us : preempt_count_sub <-irq_exit
   <...>-2265    1d..1 3419us : __do_softirq <-irq_exit
   <...>-2265    1d..1 3419us : msecs_to_jiffies <-__do_softirq
   <...>-2265    1d..1 3420us : irqtime_account_irq <-__do_softirq
   <...>-2265    1d..1 3420us : __local_bh_disable_ip <-__do_softirq
   <...>-2265    1..s1 3421us : run_timer_softirq <-__do_softirq
   <...>-2265    1..s1 3421us : hrtimer_run_pending <-run_timer_softirq
   <...>-2265    1..s1 3421us : _raw_spin_lock_irq <-run_timer_softirq
   <...>-2265    1d.s1 3422us : preempt_count_add <-_raw_spin_lock_irq
   <...>-2265    1d.s2 3422us : _raw_spin_unlock_irq <-run_timer_softirq
   <...>-2265    1..s2 3422us : preempt_count_sub <-_raw_spin_unlock_irq
   <...>-2265    1..s1 3423us : rcu_bh_qs <-__do_softirq
   <...>-2265    1d.s1 3423us : irqtime_account_irq <-__do_softirq
   <...>-2265    1d.s1 3423us : __local_bh_enable <-__do_softirq

Signed-off-by: Joel Fernandes <agnel.joel@...il.com>
---
 kernel/trace/trace_irqsoff.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index e4e5658..ca8f84f 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -110,8 +110,20 @@ static int func_prolog_dec(struct trace_array *tr,
 
 	local_save_flags(*flags);
 	/* slight chance to get a false positive on tracing_cpu */
-	if (!irqs_disabled_flags(*flags))
-		return 0;
+	switch (trace_type) {
+	case (TRACER_IRQS_OFF | TRACER_PREEMPT_OFF):
+		if (!preempt_trace() && !irqs_disabled_flags(*flags))
+			return 0;
+		break;
+	case TRACER_IRQS_OFF:
+		if (!irqs_disabled_flags(*flags))
+			return 0;
+		break;
+	case TRACER_PREEMPT_OFF:
+		if (!preempt_trace())
+			return 0;
+		break;
+	}
 
 	*data = per_cpu_ptr(tr->trace_buffer.data, cpu);
 	disabled = atomic_inc_return(&(*data)->disabled);
-- 
2.5.0