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Date:   Sun, 17 Feb 2019 08:30:25 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Qian Cai <cai@....pw>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] trace: skip hwasan

On Sun, Feb 17, 2019 at 5:34 AM Qian Cai <cai@....pw> wrote:
>
> Enabling function tracer with CONFIG_KASAN_SW_TAGS=y (hwasan) tracer
> causes the whole system frozen on ThunderX2 systems with 256 CPUs,
> because there is a burst of too much pointer access, and then KASAN will
> dereference each byte of the shadow address for the tag checking which
> will kill all the CPUs.

Hi Qian,

Could you please elaborate what exactly happens and who/why kills
CPUs? Number of memory accesses should not make any difference.
With hardware support (MTE) it won't be possible to disable
instrumentation (loads and stores check tags themselves), so it would
be useful to keep track of exact reasons we disable instrumentation to
know how to deal with them with hardware support.
It would be useful to keep this info in the comment in the Makefile.

Thanks

> Signed-off-by: Qian Cai <cai@....pw>
> ---
>  kernel/trace/Makefile | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index c2b2148bb1d2..fdd547a68385 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -28,6 +28,11 @@ ifdef CONFIG_GCOV_PROFILE_FTRACE
>  GCOV_PROFILE := y
>  endif
>
> +# Too much pointer access will kill hwasan.
> +ifdef CONFIG_KASAN_SW_TAGS
> +KASAN_SANITIZE := n
> +endif
> +
>  CFLAGS_trace_benchmark.o := -I$(src)
>  CFLAGS_trace_events_filter.o := -I$(src)
>
> --
> 2.17.2 (Apple Git-113)
>
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