From: Shreyas B. Prabhu Date: Thu, 28 May 2015 22:44:19 +0000 (-0700) Subject: tracing/mm: don't trace mm_page_free on offline cpus X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=1f0c27b50f4f2567e649f49d77daee2bbf3f40e5;p=linux-beck.git tracing/mm: don't trace mm_page_free on offline cpus 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: .dump_stack+0x98/0xd4 (unreliable) .lockdep_rcu_suspicious+0x108/0x170 .free_pages_prepare+0x494/0x680 .free_hot_cold_page+0x50/0x280 .destroy_context+0x90/0xd0 .__mmdrop+0x58/0x160 .idle_task_exit+0xf0/0x100 .pnv_smp_cpu_kill_self+0x58/0x2c0 .cpu_die+0x34/0x50 .arch_cpu_idle_dead+0x20/0x40 .cpu_startup_entry+0x708/0x7a0 .start_secondary+0x36c/0x3a0 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 Reviewed-by: Preeti U Murthy Acked-by: Steven Rostedt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h index 78efa0a197a9..aa863549e77a 100644 --- a/include/trace/events/kmem.h +++ b/include/trace/events/kmem.h @@ -158,12 +158,24 @@ DEFINE_EVENT_CONDITION(kmem_free, kmem_cache_free, TP_CONDITION(cpu_online(raw_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), + + /* + * This trace can be potentially called from an offlined cpu. + * Since trace points use RCU and RCU should not be used from + * offline cpus, filter such calls out. + * While this trace can be called from a preemptable section, + * it has no impact on the condition since tasks can migrate + * only from online cpus to other online cpus. Thus its safe + * to use raw_smp_processor_id. + */ + TP_CONDITION(cpu_online(raw_smp_processor_id())), + TP_STRUCT__entry( __field( unsigned long, pfn ) __field( unsigned int, order )