linux-kernel - Re: [PATCH] kcsan, trace: Make KCSAN compatible with tracing

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Date:   Fri, 14 Feb 2020 22:59:39 +0100
From:   Marco Elver <elver@...gle.com>
To:     Qian Cai <cai@....pw>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] kcsan, trace: Make KCSAN compatible with tracing

On Fri, 14 Feb 2020 at 20:35, Qian Cai <cai@....pw> wrote:
>
> On Fri, 2020-02-14 at 20:05 +0100, Marco Elver wrote:
> > Previously the system would lock up if ftrace was enabled together with
> > KCSAN. This is due to recursion on reporting if the tracer code is
> > instrumented with KCSAN.
> >
> > To avoid this for all types of tracing, disable KCSAN instrumentation
> > for all of kernel/trace.
>
> I remembered that KCSAN + ftrace was working last week, but I probably had a bad
> memory. Anyway, this patch works fine. Feel free to add,
>
> Tested-by: Qian Cai <cai@....pw>

Based your further feedback I've sent v2:
  http://lkml.kernel.org/r/20200214211035.209972-1-elver@google.com

Thanks,
-- Marco

> >
> > Signed-off-by: Marco Elver <elver@...gle.com>
> > Reported-by: Qian Cai <cai@....pw>
> > Cc: Paul E. McKenney <paulmck@...nel.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > ---
> >  kernel/kcsan/Makefile | 2 ++
> >  kernel/trace/Makefile | 3 +++
> >  2 files changed, 5 insertions(+)
> >
> > diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> > index df6b7799e4927..d4999b38d1be5 100644
> > --- a/kernel/kcsan/Makefile
> > +++ b/kernel/kcsan/Makefile
> > @@ -4,6 +4,8 @@ KCOV_INSTRUMENT := n
> >  UBSAN_SANITIZE := n
> >
> >  CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
> > +CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
> > +CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
> >
> >  CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
> >       $(call cc-option,-fno-stack-protector,)
> > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> > index f9dcd19165fa2..6b601d88bf71e 100644
> > --- a/kernel/trace/Makefile
> > +++ b/kernel/trace/Makefile
> > @@ -6,6 +6,9 @@ ifdef CONFIG_FUNCTION_TRACER
> >  ORIG_CFLAGS := $(KBUILD_CFLAGS)
> >  KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS))
> >
> > +# Avoid recursion due to instrumentation.
> > +KCSAN_SANITIZE := n
> > +
> >  ifdef CONFIG_FTRACE_SELFTEST
> >  # selftest needs instrumentation
> >  CFLAGS_trace_selftest_dynamic.o = $(CC_FLAGS_FTRACE)