linux-kernel - Re: [PATCH 1/2] tracing/mm: don't trace kfree on offline CPUs

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Date:	Tue, 16 Feb 2016 08:52:24 +0300
From:	Denis Kirjanov <kda@...ux-powerpc.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/2] tracing/mm: don't trace kfree on offline CPUs

On 2/15/16, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Sun, 14 Feb 2016 23:19:42 +0300
> Denis Kirjanov <kda@...ux-powerpc.org> wrote:
>
>
>> >>  	TP_PROTO(unsigned long call_site, const void *ptr),
>> >>
>> >> -	TP_ARGS(call_site, ptr)
>> >> +	TP_ARGS(call_site, ptr),
>> >> +
>> >> +	/*
>> >> +	 * This trace can be potentially called from an offlined cpu.
>> >> +	 * Since trace points use RCU and RCU should not be used from
>> >> +	 * offline cpus, filter such calls out.
>> >> +	 * While this trace can be called from a preemptable section,
>> >> +	 * it has no impact on the condition since tasks can migrate
>> >> +	 * only from online cpus to other online cpus. Thus its safe
>> >> +	 * to use raw_smp_processor_id.
>> >> +	 */
>> >> +	TP_CONDITION(cpu_online(raw_smp_processor_id()))
>> >
>> > This is starting to become a common occurrence. Perhaps it is best to
>> > just hardcode this into the tracepoint code itself?
>>
>> Can you take it as a fix for now. I'll post the follow-up patch then
>> for rcu and offline cpus
>> issue.
>
> Actually, I prefer not to add more checks for cpu_online(), if its
> going to become the default.
>
> Does this work for you instead?

Hm, somehow it doesn't work:

[   84.692846] ===============================
[   84.692847] [ INFO: suspicious RCU usage. ]
[   84.692849] 4.5.0-rc3-00765-g78b70d4-dirty #36 Tainted: G S
[   84.692850] -------------------------------
[   84.692851] include/trace/events/rcu.h:457 suspicious
rcu_dereference_check() usage!
[   84.692852]
other info that might help us debug this:

[   84.692854]
RCU used illegally from offline CPU!
rcu_scheduler_active = 1, debug_locks = 1
[   84.692855] no locks held by swapper/11/0.
[   84.692856]
stack backtrace:
[   84.692858] CPU: 11 PID: 0 Comm: swapper/11 Tainted: G S
  4.5.0-rc3-00765-g78b70d4-dirty #36
[   84.692860] Call Trace:
[   84.692868] [c0000005b76d37f0] [c0000000008c57ac]
.dump_stack+0xe0/0x14c (unreliable)
[   84.692872] [c0000005b76d3880] [c00000000010d0c8]
.lockdep_rcu_suspicious+0x108/0x170
[   84.692876] [c0000005b76d3910] [c00000000013cab4]
.__call_rcu.constprop.60+0x244/0x680
[   84.692880] [c0000005b76d39e0] [c0000000002c38ec] .put_object+0x5c/0x80
[   84.692884] [c0000005b76d3a60] [c00000000029e748]
.kmem_cache_free+0x318/0x4c0
[   84.692888] [c0000005b76d3b00] [c0000000000936b4] .__mmdrop+0x54/0x150
[   84.692891] [c0000005b76d3b90] [c0000000000e46e0] .idle_task_exit+0x120/0x130
[   84.692895] [c0000005b76d3c20] [c000000000075a14]
.pseries_mach_cpu_die+0x64/0x310
[   84.692899] [c0000005b76d3cd0] [c00000000004401c] .cpu_die+0x3c/0x60
[   84.692902] [c0000005b76d3d40] [c000000000018998]
.arch_cpu_idle_dead+0x28/0x40
[   84.692906] [c0000005b76d3db0] [c000000000102714]
.cpu_startup_entry+0x554/0x580
[   84.692909] [c0000005b76d3ed0] [c000000000043d68]
.start_secondary+0x348/0x390
[   84.692913] [c0000005b76d3f90] [c000000000008a6c]
start_secondary_prolog+0x10/0x14

[   84.692918] ===============================
[   84.692919] [ INFO: suspicious RCU usage. ]
[   84.692920] 4.5.0-rc3-00765-g78b70d4-dirty #36 Tainted: G S
[   84.692921] -------------------------------
[   84.692922] include/trace/events/kmem.h:141 suspicious
rcu_dereference_check() usage!
[   84.692923]
other info that might help us debug this:

[   84.692924]
RCU used illegally from offline CPU!
rcu_scheduler_active = 1, debug_locks = 1
[   84.692925] no locks held by swapper/11/0.
[   84.692926]
stack backtrace:
[   84.692928] CPU: 11 PID: 0 Comm: swapper/11 Tainted: G S
  4.5.0-rc3-00765-g78b70d4-dirty #36
[   84.692929] Call Trace:
[   84.692933] [c0000005b76d38c0] [c0000000008c57ac]
.dump_stack+0xe0/0x14c (unreliable)
[   84.692936] [c0000005b76d3950] [c00000000010d0c8]
.lockdep_rcu_suspicious+0x108/0x170
[   84.692939] [c0000005b76d39e0] [c00000000029f1c0] .kfree+0x380/0x470
[   84.692942] [c0000005b76d3a80] [c000000000056194] .destroy_context+0x44/0x100
[   84.692946] [c0000005b76d3b00] [c0000000000936c0] .__mmdrop+0x60/0x150
[   84.692948] [c0000005b76d3b90] [c0000000000e46e0] .idle_task_exit+0x120/0x130
[   84.692951] [c0000005b76d3c20] [c000000000075a14]
.pseries_mach_cpu_die+0x64/0x310
[   84.692954] [c0000005b76d3cd0] [c00000000004401c] .cpu_die+0x3c/0x60
[   84.692957] [c0000005b76d3d40] [c000000000018998]
.arch_cpu_idle_dead+0x28/0x40
[   84.692960] [c0000005b76d3db0] [c000000000102714]
.cpu_startup_entry+0x554/0x580
[   84.692963] [c0000005b76d3ed0] [c000000000043d68]
.start_secondary+0x348/0x390
[   84.692966] [c0000005b76d3f90] [c000000000008a6c]
start_secondary_prolog+0x10/0x14



>
> -- Steve
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index acd522a91539..acfdbf353a0b 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -14,8 +14,10 @@
>   * See the file COPYING for more details.
>   */
>
> +#include <linux/smp.h>
>  #include <linux/errno.h>
>  #include <linux/types.h>
> +#include <linux/cpumask.h>
>  #include <linux/rcupdate.h>
>  #include <linux/tracepoint-defs.h>
>
> @@ -132,6 +134,9 @@ extern void syscall_unregfunc(void);
>  		void *it_func;						\
>  		void *__data;						\
>  									\
> +		if (!cpu_online(raw_smp_processor_id()))		\
> +			return;						\
> +									\
>  		if (!(cond))						\
>  			return;						\
>  		prercu;							\
>