Re: [PATCH 2/2] x86/tbl/trace: Do not trace on CPU that is offline

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Fri, Feb 06, 2015 at 03:06:55PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
> 
> When taking a CPU down for suspend and resume, a tracepoint may be called
> when the CPU has been designated offline. As tracepoints require RCU for
> protection, they must not be called if the current CPU is offline.
> 
> Unfortunately, trace_tlb_flush() is called in this scenario as was noted
> by LOCKDEP:
> 
> ...
> 
>  Disabling non-boot CPUs ...
>  intel_pstate CPU 1 exiting
> 
>  ===============================
>  smpboot: CPU 1 didn't die...
>  [ INFO: suspicious RCU usage. ]
>  3.19.0-rc7-next-20150204.1-iniza-small #1 Not tainted
>  -------------------------------
>  include/trace/events/tlb.h:35 suspicious rcu_dereference_check() usage!
> 
>  other info that might help us debug this:
> 
>  RCU used illegally from offline CPU!
>  rcu_scheduler_active = 1, debug_locks = 0
>  no locks held by swapper/1/0.
> 
>  stack backtrace:
>  CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.19.0-rc7-next-20150204.1-iniza-small #1
>  Hardware name: SAMSUNG ELECTRONICS CO., LTD. 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
>   0000000000000001 ffff88011a44fe18 ffffffff817e370d 0000000000000011
>   ffff88011a448290 ffff88011a44fe48 ffffffff810d6847 ffff8800c66b9600
>   0000000000000001 ffff88011a44c000 ffffffff81cb3900 ffff88011a44fe78
>  Call Trace:
>   [<ffffffff817e370d>] dump_stack+0x4c/0x65
>   [<ffffffff810d6847>] lockdep_rcu_suspicious+0xe7/0x120
>   [<ffffffff810b71a5>] idle_task_exit+0x205/0x2c0
>   [<ffffffff81054c4e>] play_dead_common+0xe/0x50
>   [<ffffffff81054ca5>] native_play_dead+0x15/0x140
>   [<ffffffff8102963f>] arch_cpu_idle_dead+0xf/0x20
>   [<ffffffff810cd89e>] cpu_startup_entry+0x37e/0x580
>   [<ffffffff81053e20>] start_secondary+0x140/0x150
>  intel_pstate CPU 2 exiting
> 
> ...
> 
> By converting the tlb_flush tracepoint to a TRACE_EVENT_CONDITION where the
> condition is cpu_online(smp_processor_id()), we can avoid calling RCU protected
> code when the CPU is offline.
> 
> Link: http://lkml.kernel.org/r/CA+icZUUGiGDoL5NU8RuxKzFjoLjEKRtUWx=JB8B9a0EQv-eGzQ@mail.gmail.com
> 
> Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
> Suggested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
>  include/trace/events/tlb.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/trace/events/tlb.h b/include/trace/events/tlb.h
> index 13391d288107..0e7635765153 100644
> --- a/include/trace/events/tlb.h
> +++ b/include/trace/events/tlb.h
> @@ -13,11 +13,13 @@
>  	{ TLB_LOCAL_SHOOTDOWN,		"local shootdown" },		\
>  	{ TLB_LOCAL_MM_SHOOTDOWN,	"local mm shootdown" }
> 
> -TRACE_EVENT(tlb_flush,
> +TRACE_EVENT_CONDITION(tlb_flush,
> 
>  	TP_PROTO(int reason, unsigned long pages),
>  	TP_ARGS(reason, pages),
> 
> +	TP_CONDITION(cpu_online(smp_processor_id())),
> +
>  	TP_STRUCT__entry(
>  		__field(	  int, reason)
>  		__field(unsigned long,  pages)
> -- 
> 2.1.4
> 
>