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

[Qian Cai]

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@xxxxxx>

> 
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> Reported-by: Qian Cai <cai@xxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> ---
>  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)