Patch "tracepoints: Do not trace when cpu is offline" has been added to the 4.4-stable tree
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This is a note to let you know that I've just added the patch titled
tracepoints: Do not trace when cpu is offline
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracepoints-do-not-trace-when-cpu-is-offline.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.
Quoted 1 line
From
f37755490fe9bf76f6ba1d8c6591745d3574a6a6Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <[email protected]>
Date: Mon, 15 Feb 2016 12:36:14 -0500
Subject: tracepoints: Do not trace when cpu is offline
From: Steven Rostedt (Red Hat) <[email protected]>
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.
--- include/linux/tracepoint.h | 5 +++++ 1 file changed, 5 insertions(+)
include/linux/tracepoint.h +5 -0
@@ -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>
@@ -146,6 +148,9 @@ extern void syscall_unregfunc(void);void *it_func; \void *__data; \ \ +if (!cpu_online (raw_smp_processor_id ())) \ +return ; \ + \if (!(cond)) \return ; \ prercu; \
Patches currently in stable-queue which might be from [email protected] are
queue-4.4/tools-lib-traceevent-fix-output-of-llu-for-64-bit-values-read-on-32-bit-machines.patch queue-4.4/tracing-fix-freak-link-error-caused-by-branch-tracer.patch queue-4.4/tracepoints-do-not-trace-when-cpu-is-offline.patch