Re: FAILED: patch "[PATCH] tracepoints: Do not trace when cpu is offline" failed to apply to 3.14-stable tree

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 23 Feb 2016 16:48:47 -0800
<gregkh@linuxfoundation.org> wrote:

> The patch below does not apply to the 3.14-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Hmm, strange. I just checked out v3.14.60 and did:

 $ git cherry-pick f37755490fe9bf76f6ba1d8c6591745d3574a6a6

and it applied without issue.

Below is the result.

-- Steve

> 
> thanks,
> 
> greg k-h
> 
> ------------------ original commit in Linus's tree ------------------
> 
> >From f37755490fe9bf76f6ba1d8c6591745d3574a6a6 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
> 
>


>From 5921fea2b95c0795d88f7b82633242c341be2efc 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

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>
---
 include/linux/tracepoint.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 7159a0a..8e344f6 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>
 
@@ -126,6 +128,9 @@ static inline void tracepoint_synchronize_unregister(void)
 		void *it_func;						\
 		void *__data;						\
 									\
+		if (!cpu_online(raw_smp_processor_id()))		\
+			return;						\
+									\
 		if (!(cond))						\
 			return;						\
 		prercu;							\
-- 
2.7.0