Re: [PATCH v2 2/2] tracing/rcu: don't trace rcu_callback on offline CPUs

[Paul E. McKenney]

On Sun, Feb 14, 2016 at 09:50:18AM +0300, Denis Kirjanov wrote:
> Tracepoints use RCU for protection and they must not be called on
> offline CPUS. So make this tracepoint conditional.

Good catch!  Queued for review and testing.

							Thanx, Paul

> NFO: suspicious RCU usage. ]
> [  413.344670] 4.4.0-00006-g0fe53e8-dirty #33 Tainted: G S
> [  413.344672] -------------------------------
> [  413.344673] include/trace/events/rcu.h:457 suspicious rcu_dereference_check() usage!
> [  413.344674]
> other info that might help us debug this:
> 
> [  413.344676]
> RCU used illegally from offline CPU!
> rcu_scheduler_active = 1, debug_locks = 1
> [  413.344678] no locks held by swapper/4/0.
> [  413.344679]
> stack backtrace:
> [  413.344682] CPU: 4 PID: 0 Comm: swapper/4 Tainted: G S              4.4.0-00006-g0fe53e8-dirty #33
> [  413.344683] Call Trace:
> [  413.344692] [c0000005b76b7800] [c0000000008bb080] .dump_stack+0x98/0xd4 (unreliable)
> [  413.344698] [c0000005b76b7880] [c00000000010c8b8] .lockdep_rcu_suspicious+0x108/0x170
> [  413.344703] [c0000005b76b7910] [c00000000013b9e4] .__call_rcu.constprop.60+0x264/0x600
> [  413.344708] [c0000005b76b79e0] [c0000000002bceec] .put_object+0x5c/0x80
> [  413.344712] [c0000005b76b7a60] [c00000000029a368] .kmem_cache_free+0x298/0x450
> [  413.344716] [c0000005b76b7b00] [c000000000093494] .__mmdrop+0x54/0x150
> [  413.344720] [c0000005b76b7b90] [c0000000000e4010] .idle_task_exit+0x130/0x140
> [  413.344725] [c0000005b76b7c20] [c000000000075804] .pseries_mach_cpu_die+0x64/0x310
> [  413.344730] [c0000005b76b7cd0] [c000000000043e7c] .cpu_die+0x3c/0x60
> [  413.344734] [c0000005b76b7d40] [c0000000000188d8] .arch_cpu_idle_dead+0x28/0x40
> [  413.344738] [c0000005b76b7db0] [c000000000101e8c] .cpu_startup_entry+0x50c/0x560
> [  413.344741] [c0000005b76b7ed0] [c000000000043bd8] .start_secondary+0x328/0x360
> [  413.344746] [c0000005b76b7f90] [c000000000008a6c] start_secondary_prolog+0x10/0x14
> 
> Signed-off-by: Denis Kirjanov <kda@xxxxxxxxxxxxxxxxx>
> ---
> 
> v2: Fix the build error that was made
> while sending the pacthes from another machine
> 
>  include/trace/events/rcu.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
> index ef72c4a..793d306b 100644
> --- a/include/trace/events/rcu.h
> +++ b/include/trace/events/rcu.h
> @@ -428,13 +428,15 @@ TRACE_EVENT(rcu_prep_idle,
>   * number of lazy callbacks queued, and the fourth element is the
>   * total number of callbacks queued.
>   */
> -TRACE_EVENT(rcu_callback,
> +TRACE_EVENT_CONDITION(rcu_callback,
> 
>  	TP_PROTO(const char *rcuname, struct rcu_head *rhp, long qlen_lazy,
>  		 long qlen),
> 
>  	TP_ARGS(rcuname, rhp, qlen_lazy, qlen),
> 
> +	TP_CONDITION(cpu_online(raw_smp_processor_id())),
> +
>  	TP_STRUCT__entry(
>  		__field(const char *, rcuname)
>  		__field(void *, rhp)
> -- 
> 2.4.0
>