[PATCH 2/3] tracing/mm: Don't trace mm_page_free 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_free 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:170 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
 no locks held by swapper/1/0.

stack backtrace:
 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.1.0-rc1+ #9
 Call Trace:
 [c000001fed2f7790] [c0000000009dee8c] .dump_stack+0x98/0xd4 (unreliable)
 [c000001fed2f7810] [c000000000128d88] .lockdep_rcu_suspicious+0x108/0x170
 [c000001fed2f78a0] [c000000000203bc4] .free_pages_prepare+0x494/0x680
 [c000001fed2f7980] [c000000000207fd0] .free_hot_cold_page+0x50/0x280
 [c000001fed2f7a30] [c00000000004d000] .destroy_context+0x90/0xd0
 [c000001fed2f7ab0] [c0000000000bd1d8] .__mmdrop+0x58/0x160
 [c000001fed2f7b40] [c0000000001068e0] .idle_task_exit+0xf0/0x100
 [c000001fed2f7bc0] [c000000000066948] .pnv_smp_cpu_kill_self+0x58/0x2c0
 [c000001fed2f7ca0] [c00000000003ce34] .cpu_die+0x34/0x50
 [c000001fed2f7d10] [c0000000000176d0] .arch_cpu_idle_dead+0x20/0x40
 [c000001fed2f7d80] [c00000000011f9a8] .cpu_startup_entry+0x708/0x7a0
 [c000001fed2f7ec0] [c00000000003cb6c] .start_secondary+0x36c/0x3a0
 [c000001fed2f7f90] [c000000000008b6c] start_secondary_prolog+0x10/0x14

Fix this by converting mm_page_free 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 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
index dd9e612..4abda92 100644
--- a/include/trace/events/kmem.h
+++ b/include/trace/events/kmem.h
@@ -149,12 +149,14 @@ DEFINE_EVENT_CONDITION(kmem_free, kmem_cache_free,
 	TP_CONDITION(cpu_online(smp_processor_id()))
 );
 
-TRACE_EVENT(mm_page_free,
+TRACE_EVENT_CONDITION(mm_page_free,
 
 	TP_PROTO(struct page *page, unsigned int order),
 
 	TP_ARGS(page, order),
 
+	TP_CONDITION(cpu_online(smp_processor_id())),
+
 	TP_STRUCT__entry(
 		__field(	unsigned long,	pfn		)
 		__field(	unsigned int,	order		)
-- 
1.9.3