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

Paul E. McKenney
2015-02-06T23:27:54Z

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
>
>