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

[Denis Kirjanov]

Tracepoints use RCU for protection and they must not be called on
offline CPUS. So make this tracepoint conditional.

INFO: 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>
---
 include/trace/events/rcu.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index ef72c4a..5470f2f 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -435,6 +435,8 @@ TRACE_EVENT(rcu_callback,
 
 	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