linux-kernel - [RFC][PATCH 0/5] perf/tracing/cpuhotplug: Fix locking order

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Message-Id: <20170512171544.100715273@goodmis.org>
Date:   Fri, 12 May 2017 13:15:44 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [RFC][PATCH 0/5] perf/tracing/cpuhotplug: Fix locking order

NOTE: This was quickly written. The change logs and patches probably need
some loving. This is for discussion. These may become legitimate patches,
but for now, I'm seeing if this is an acceptable solution.

Also note, I checked out the last branch that I had Linus pull, and then
merged with tip's commit b53e5129~1, which is the commit just before
"trace/perf: Cure hotplug lock ordering issues" in tip/smp/hotplug
that placed get_online_cpus() ahead of event_mutex. The issue is that
event_mutex is a high level mutex, and trying to make sure that
get_online_cpus() is held whenever it is held and is going to be a
nightmare. So I started ahead of that commit, but I needed changes
in my own repo to do full testing. I renamed this temp branch to
"tip/cpuhotplug", and you can pull it as well. But this is not going
to be a candidate for pushing to Linus.

The 5 patches here are:

 1) fix a lockdep splat when taking stack trace in irqsoff tracing
    (one of my tests triggered this)

 2) Allow for get_online_cpus() to nest

 3) Have kprobes take get_online_cpus() before taking jump label lock.

 4) Have tracepoints always take get_online_cpus

 5) Have perf take event_mutex before taking get_online_cpus()

Thoughts?

-- Steve

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/cpuhotplug

Head SHA1: ddb06e08fa10ed5030285267a9b1e25d40c337c8

Steven Rostedt (VMware) (5):
      tracing: Make sure RCU is watching before calling a stack trace
      cpu-hotplug: Allow get_online_cpus() to nest
      kprobes: Take get_online_cpus() before taking jump_label_lock()
      tracepoints: Grab get_online_cpus() before taking tracepoints_mutex
      perf: Grab event_mutex before taking get_online_cpus()

----
 include/linux/sched.h           | 1 +
 include/linux/trace_events.h    | 2 ++
 kernel/cpu.c                    | 9 +++++++++
 kernel/events/core.c            | 9 +++++++++
 kernel/fork.c                   | 1 +
 kernel/kprobes.c                | 6 +++---
 kernel/trace/trace.c            | 5 +++++
 kernel/trace/trace.h            | 1 -
 kernel/trace/trace_event_perf.c | 8 ++++----
 kernel/tracepoint.c             | 5 +++++
 10 files changed, 39 insertions(+), 8 deletions(-)