Re: [PATCH v2 11/11] lockdep,trace: Expose tracepoints

[Guenter Roeck]

On 9/2/20 1:56 AM, peterz@xxxxxxxxxxxxx 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.

Guenter

> ---
> 
> 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 598fec9f9dbf..997472c662c4 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -164,7 +164,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  		void *__data;						\
>  		int __maybe_unused __idx = 0;				\
>  									\
> -		if (!(cond))						\
> +		if (!(cond) || (preempt_count() & RCUIDLE_MASK))	\
>  			return;						\
>  									\
>  		/* srcu can't be used from NMI */			\
> 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
>