Re: [RFC patch powerpc,trace] Avoid suspicious RCU usage reporting for some tracepoints
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: 2012-09-10 05:10:30
On Mon, 2012-09-10 at 12:58 +0800, Li Zhong wrote:
There are a few tracepoints in the interrupt code path, which is before irq_enter(), or after irq_exit(), like trace_irq_entry()/trace_irq_exit() in do_IRQ(), trace_timer_interrupt_entry()/trace_timer_interrupt_exit() in timer_interrupt(). If the interrupt is from idle(), and because tracepoint contains RCU read-side critical section, we could see following suspicious RCU usage reported:
.../...
This is because the RCU usage in interrupt context should be used in area marked by rcu_irq_enter()/rcu_irq_exit(), called in irq_enter()/irq_exit() respectively. Could we add a new tracepoint trace_***_rcuirq, like trace_***_rcuidle to avoid the report? like the code attached below. Or could we just move these tracepoints inside the irq_enter()/irq_exit() area? (Seems not good for the timer_interrupt case).
I'd say just move them in. Anton, any objection ?
quoted hunk ↗ jump to hunk
Thanks, Zhong Signed-off-by: Li Zhong <redacted> --- arch/powerpc/kernel/irq.c | 4 ++-- arch/powerpc/kernel/time.c | 4 ++-- include/linux/tracepoint.h | 10 ++++++++++ 3 files changed, 14 insertions(+), 4 deletions(-)diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c index 1f017bb..f0ac4e7 100644 --- a/arch/powerpc/kernel/irq.c +++ b/arch/powerpc/kernel/irq.c@@ -489,7 +489,7 @@ void do_IRQ(struct pt_regs *regs) struct pt_regs *old_regs = set_irq_regs(regs); unsigned int irq; - trace_irq_entry(regs); + trace_irq_entry_rcuirq(regs); irq_enter();@@ -514,7 +514,7 @@ void do_IRQ(struct pt_regs *regs) irq_exit(); set_irq_regs(old_regs); - trace_irq_exit(regs); + trace_irq_exit_rcuirq(regs); } void __init init_IRQ(void)diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index e49e931..cbd6607 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c@@ -493,7 +493,7 @@ void timer_interrupt(struct pt_regs * regs) */ may_hard_irq_enable(); - trace_timer_interrupt_entry(regs); + trace_timer_interrupt_entry_rcuirq(regs); __get_cpu_var(irq_stat).timer_irqs++;@@ -532,7 +532,7 @@ void timer_interrupt(struct pt_regs * regs) irq_exit(); set_irq_regs(old_regs); - trace_timer_interrupt_exit(regs); + trace_timer_interrupt_exit_rcuirq(regs); } /*diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 802de56..f7672d5 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h@@ -161,6 +161,16 @@ static inline void tracepoint_synchronize_unregister(void) rcu_idle_exit(), \ rcu_idle_enter()); \ } \ + static inline void trace_##name##_rcuirq(proto) \ + { \ + if (static_key_false(&__tracepoint_##name.key)) \ + __DO_TRACE(&__tracepoint_##name, \ + TP_PROTO(data_proto), \ + TP_ARGS(data_args), \ + TP_CONDITION(cond), \ + rcu_irq_enter(), \ + rcu_irq_exit()); \ + } \ static inline int \ register_trace_##name(void (*probe)(data_proto), void *data) \ { \