[PATCH 3/3] tracing/mm: Don't trace mm_page_pcpu_drain on offline cpus

["Shreyas B. Prabhu" <shreyas@linux.vnet.ibm.com>]

Since tracepoints use RCU for protection, they must not be called on
offline cpus. trace_mm_page_pcpu_drain can be called on an offline cpu
in this scenario caught by LOCKDEP:

 ===============================
 [ INFO: suspicious RCU usage. ]
 4.1.0-rc1+ #9 Not tainted
 -------------------------------
 include/trace/events/kmem.h:265 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 = 1
 1 lock held by swapper/5/0:
  #0:  (&(&zone->lock)->rlock){..-...}, at: [<c0000000002073b0>] .free_pcppages_bulk+0x70/0x920

stack backtrace:
 CPU: 5 PID: 0 Comm: swapper/5 Not tainted 4.1.0-rc1+ #9
 Call Trace:
 [c000001fed2e7720] [c0000000009dee8c] .dump_stack+0x98/0xd4 (unreliable)
 [c000001fed2e77a0] [c000000000128d88] .lockdep_rcu_suspicious+0x108/0x170
 [c000001fed2e7830] [c00000000020794c] .free_pcppages_bulk+0x60c/0x920
 [c000001fed2e7980] [c000000000208188] .free_hot_cold_page+0x208/0x280
 [c000001fed2e7a30] [c00000000004d000] .destroy_context+0x90/0xd0
 [c000001fed2e7ab0] [c0000000000bd1d8] .__mmdrop+0x58/0x160
 [c000001fed2e7b40] [c0000000001068e0] .idle_task_exit+0xf0/0x100
 [c000001fed2e7bc0] [c000000000066948] .pnv_smp_cpu_kill_self+0x58/0x2c0
 [c000001fed2e7ca0] [c00000000003ce34] .cpu_die+0x34/0x50
 [c000001fed2e7d10] [c0000000000176d0] .arch_cpu_idle_dead+0x20/0x40
 [c000001fed2e7d80] [c00000000011f9a8] .cpu_startup_entry+0x708/0x7a0
 [c000001fed2e7ec0] [c00000000003cb6c] .start_secondary+0x36c/0x3a0
 [c000001fed2e7f90] [c000000000008b6c] start_secondary_prolog+0x10/0x14

Fix this by converting mm_page_pcpu_drain trace point into TRACE_EVENT_CONDITION
where condition is cpu_online(smp_processor_id())

Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
---
 include/trace/events/kmem.h | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
index 4abda92..6cd975f 100644
--- a/include/trace/events/kmem.h
+++ b/include/trace/events/kmem.h
@@ -257,12 +257,26 @@ DEFINE_EVENT(mm_page, mm_page_alloc_zone_locked,
 	TP_ARGS(page, order, migratetype)
 );
 
-DEFINE_EVENT_PRINT(mm_page, mm_page_pcpu_drain,
+TRACE_EVENT_CONDITION(mm_page_pcpu_drain,
 
 	TP_PROTO(struct page *page, unsigned int order, int migratetype),
 
 	TP_ARGS(page, order, migratetype),
 
+	TP_CONDITION(cpu_online(smp_processor_id())),
+
+	TP_STRUCT__entry(
+		__field(	unsigned long,	pfn		)
+		__field(	unsigned int,	order		)
+		__field(	int,		migratetype	)
+	),
+
+	TP_fast_assign(
+		__entry->pfn		= page ? page_to_pfn(page) : -1UL;
+		__entry->order		= order;
+		__entry->migratetype	= migratetype;
+	),
+
 	TP_printk("page=%p pfn=%lu order=%d migratetype=%d",
 		pfn_to_page(__entry->pfn), __entry->pfn,
 		__entry->order, __entry->migratetype)
-- 
1.9.3