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Date: Thu, 3 Sep 2020 16:00:47 +0200
From: peterz@...radead.org
To: Guenter Roeck <linux@...ck-us.net>
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, will@...nel.org,
npiggin@...il.com, elver@...gle.com, jgross@...e.com,
paulmck@...nel.org, rostedt@...dmis.org, rjw@...ysocki.net,
joel@...lfernandes.org, svens@...ux.ibm.com, tglx@...utronix.de,
ulf.hansson@...aro.org, viresh.kumar@...aro.org,
vincent.guittot@...aro.org
Subject: Re: [PATCH v2 11/11] lockdep,trace: Expose tracepoints
On Wed, Sep 02, 2020 at 06:57:36AM -0700, Guenter Roeck wrote:
> On 9/2/20 1:56 AM, peterz@...radead.org wrote:
> > On Tue, Sep 01, 2020 at 08:51:46PM -0700, Guenter Roeck wrote:
> >
> >> [ 27.056457] include/trace/events/lock.h:13 suspicious rcu_dereference_check() usage!
> >
> >> [ 27.057006] Hardware name: Generic OMAP3-GP (Flattened Device Tree)
> >> [ 27.057098] [<c03125b4>] (unwind_backtrace) from [<c030c32c>] (show_stack+0x10/0x14)
> >> [ 27.057189] [<c030c32c>] (show_stack) from [<c08e7a4c>] (dump_stack+0xd8/0xf8)
> >> [ 27.057312] [<c08e7a4c>] (dump_stack) from [<c03b04bc>] (lock_acquire+0x4d8/0x4dc)
> >> [ 27.057464] [<c03b04bc>] (lock_acquire) from [<c12457e8>] (_raw_spin_lock_irqsave+0x58/0x74)
> >> [ 27.057617] [<c12457e8>] (_raw_spin_lock_irqsave) from [<c0338198>] (pwrdm_lock+0x10/0x18)
> >> [ 27.057739] [<c0338198>] (pwrdm_lock) from [<c033a214>] (clkdm_deny_idle+0x10/0x24)
> >> [ 27.057891] [<c033a214>] (clkdm_deny_idle) from [<c0332e10>] (omap3_enter_idle_bm+0xd4/0x1b8)
> >> [ 27.058044] [<c0332e10>] (omap3_enter_idle_bm) from [<c0f740d4>] (cpuidle_enter_state+0x16c/0x620)
> >
> > ARM cpuidle is a trainwreck :/
> >
> > So it looks like we have:
> >
> > - clkdm_
> > - pwrdm_
> > - cpu_pm_
> > - pm_runtime_
> >
> > In that approximate order, and then there's the coupled idle muck.
> > Sometimes cpuidle core calls cpu_pm_*(), but mostly it's sprinkled
> > around in drivers.
> >
> > How about we unconditionally kill tracing when RCU is idle? Yes this is
> > a hack, and we really should turn it into a WARN in due time.
> >
> > The thing is, we're shutting down clock/power domains and god knows
> > what, the CPU is in a crap state, we'll not take interrupts, but tracing
> > must happen! Hell no.
> >
> > Let's make the rule that if you want something traced, you get to pull
> > it out of the cpuidle driver and stick it in the generic code with a
> > CPUIDLE_FLAG, before rcu_idle_enter().
> >
> > Totally untested patch below..
> >
>
> Unfortunately, that patch does not make a difference; I still see the
> same tracebacks with it applied.
I stuck a tracepoint in intel_idle and had a rummage around. The below
seems to work for me now.
---
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 7d9c1c0e149c..878bac893e41 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -27,17 +27,20 @@
* SOFTIRQ_MASK: 0x0000ff00
* HARDIRQ_MASK: 0x000f0000
* NMI_MASK: 0x00f00000
+ * RCUIDLE_MASK: 0x01000000
* PREEMPT_NEED_RESCHED: 0x80000000
*/
#define PREEMPT_BITS 8
#define SOFTIRQ_BITS 8
#define HARDIRQ_BITS 4
#define NMI_BITS 4
+#define RCUIDLE_BITS 1
#define PREEMPT_SHIFT 0
#define SOFTIRQ_SHIFT (PREEMPT_SHIFT + PREEMPT_BITS)
#define HARDIRQ_SHIFT (SOFTIRQ_SHIFT + SOFTIRQ_BITS)
#define NMI_SHIFT (HARDIRQ_SHIFT + HARDIRQ_BITS)
+#define RCUIDLE_SHIFT (NMI_SHIFT + NMI_BITS)
#define __IRQ_MASK(x) ((1UL << (x))-1)
@@ -45,11 +48,13 @@
#define SOFTIRQ_MASK (__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
#define HARDIRQ_MASK (__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
#define NMI_MASK (__IRQ_MASK(NMI_BITS) << NMI_SHIFT)
+#define RCUIDLE_MASK (__IRQ_MASK(RCUIDLE_BITS) << RCUIDLE_SHIFT)
#define PREEMPT_OFFSET (1UL << PREEMPT_SHIFT)
#define SOFTIRQ_OFFSET (1UL << SOFTIRQ_SHIFT)
#define HARDIRQ_OFFSET (1UL << HARDIRQ_SHIFT)
#define NMI_OFFSET (1UL << NMI_SHIFT)
+#define RCUIDLE_OFFSET (1UL << RCUIDLE_SHIFT)
#define SOFTIRQ_DISABLE_OFFSET (2 * SOFTIRQ_OFFSET)
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 3722a10fc46d..5bc45f6750f5 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -172,12 +172,18 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
int __maybe_unused __idx = 0; \
void *__data; \
\
- if (!(cond)) \
+ if (!(cond) || (preempt_count() & RCUIDLE_MASK)) \
return; \
\
/* srcu can't be used from NMI */ \
WARN_ON_ONCE(rcuidle && in_nmi()); \
\
+ if (IS_ENABLED(CONFIG_LOCKDEP) && !(rcuidle)) { \
+ rcu_read_lock_sched_notrace(); \
+ rcu_dereference_sched(__tracepoint_##name.funcs);\
+ rcu_read_unlock_sched_notrace(); \
+ } \
+ \
/* keep srcu and sched-rcu usage consistent */ \
preempt_disable_notrace(); \
\
@@ -242,11 +248,6 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
TP_PROTO(data_proto), \
TP_ARGS(data_args), \
TP_CONDITION(cond), 0); \
- if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
- rcu_read_lock_sched_notrace(); \
- rcu_dereference_sched(__tracepoint_##name.funcs);\
- rcu_read_unlock_sched_notrace(); \
- } \
} \
__DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args), \
PARAMS(cond), PARAMS(data_proto), PARAMS(data_args)) \
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8ce77d9ac716..ad9fb4f12c63 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -269,6 +269,8 @@ static noinstr void rcu_dynticks_eqs_enter(void)
/* Better not have special action (TLB flush) pending! */
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
(seq & RCU_DYNTICK_CTRL_MASK));
+
+ __preempt_count_add(RCUIDLE_OFFSET);
}
/*
@@ -281,6 +283,8 @@ static noinstr void rcu_dynticks_eqs_exit(void)
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
int seq;
+ __preempt_count_sub(RCUIDLE_OFFSET);
+
/*
* CPUs seeing atomic_add_return() must see prior idle sojourns,
* and we also must force ordering with the next RCU read-side
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