Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759742AbcCDJpZ (ORCPT ); Fri, 4 Mar 2016 04:45:25 -0500 Received: from mx2.suse.de ([195.135.220.15]:59797 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758906AbcCDJC7 (ORCPT ); Fri, 4 Mar 2016 04:02:59 -0500 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, "Steven Rostedt (Red Hat)" , Jiri Slaby Subject: [PATCH 3.12 027/116] tracepoints: Do not trace when cpu is offline Date: Fri, 4 Mar 2016 10:01:12 +0100 Message-Id: X-Mailer: git-send-email 2.7.2 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3499 Lines: 92 From: "Steven Rostedt (Red Hat)" 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit f37755490fe9bf76f6ba1d8c6591745d3574a6a6 upstream. The tracepoint infrastructure uses RCU sched protection to enable and disable tracepoints safely. There are some instances where tracepoints are used in infrastructure code (like kfree()) that get called after a CPU is going offline, and perhaps when it is coming back online but hasn't been registered yet. This can probuce the following warning: [ INFO: suspicious RCU usage. ] 4.4.0-00006-g0fe53e8-dirty #34 Tainted: G S ------------------------------- include/trace/events/kmem.h:141 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/8/0. stack backtrace: CPU: 8 PID: 0 Comm: swapper/8 Tainted: G S 4.4.0-00006-g0fe53e8-dirty #34 Call Trace: [c0000005b76c78d0] [c0000000008b9540] .dump_stack+0x98/0xd4 (unreliable) [c0000005b76c7950] [c00000000010c898] .lockdep_rcu_suspicious+0x108/0x170 [c0000005b76c79e0] [c00000000029adc0] .kfree+0x390/0x440 [c0000005b76c7a80] [c000000000055f74] .destroy_context+0x44/0x100 [c0000005b76c7b00] [c0000000000934a0] .__mmdrop+0x60/0x150 [c0000005b76c7b90] [c0000000000e3ff0] .idle_task_exit+0x130/0x140 [c0000005b76c7c20] [c000000000075804] .pseries_mach_cpu_die+0x64/0x310 [c0000005b76c7cd0] [c000000000043e7c] .cpu_die+0x3c/0x60 [c0000005b76c7d40] [c0000000000188d8] .arch_cpu_idle_dead+0x28/0x40 [c0000005b76c7db0] [c000000000101e6c] .cpu_startup_entry+0x50c/0x560 [c0000005b76c7ed0] [c000000000043bd8] .start_secondary+0x328/0x360 [c0000005b76c7f90] [c000000000008a6c] start_secondary_prolog+0x10/0x14 This warning is not a false positive either. RCU is not protecting code that is being executed while the CPU is offline. Instead of playing "whack-a-mole(TM)" and adding conditional statements to the tracepoints we find that are used in this instance, simply add a cpu_online() test to the tracepoint code where the tracepoint will be ignored if the CPU is offline. Use of raw_smp_processor_id() is fine, as there should never be a case where the tracepoint code goes from running on a CPU that is online and suddenly gets migrated to a CPU that is offline. Link: http://lkml.kernel.org/r/1455387773-4245-1-git-send-email-kda@linux-powerpc.org Reported-by: Denis Kirjanov Fixes: 97e1c18e8d17b ("tracing: Kernel Tracepoints") Signed-off-by: Steven Rostedt Signed-off-by: Jiri Slaby --- include/linux/tracepoint.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 0ecc46e7af3d..c1248996006f 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -14,8 +14,11 @@ * See the file COPYING for more details. */ +#include #include #include +#include +#include #include #include @@ -126,6 +129,9 @@ static inline void tracepoint_synchronize_unregister(void) void *it_func; \ void *__data; \ \ + if (!cpu_online(raw_smp_processor_id())) \ + return; \ + \ if (!(cond)) \ return; \ prercu; \ -- 2.7.2