From 5b163dd04f4640bfc3a971d1a8ce09540dfc10aa Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
Date: Mon, 15 Feb 2016 12:36:14 -0500
Subject: [PATCH] tracepoints: Do not trace when cpu is offline
[ Upstream commit f37755490fe9bf76f6ba1d8c6591745d3574a6a6 ]
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 <kda@linux-powerpc.org>
Fixes: 97e1c18e8d17b ("tracing: Kernel Tracepoints")
Cc: stable@vger.kernel.org # v2.6.28+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
include/linux/tracepoint.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index c72851328ca9..72486551c4ca 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -14,8 +14,10 @@
* See the file COPYING for more details.
*/
+#include <linux/smp.h>
#include <linux/errno.h>
#include <linux/types.h>
+#include <linux/cpumask.h>
#include <linux/rcupdate.h>
#include <linux/static_key.h>
@@ -121,6 +123,9 @@ extern void syscall_unregfunc(void);
void *it_func; \
void *__data; \
\
+ if (!cpu_online(raw_smp_processor_id())) \
+ return; \
+ \
if (!(cond)) \
return; \
prercu; \
--
2.30.9