linux-kernel - Re: [PATCH] x86/unwind_guess: Prevent using UNWINDER

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Date:   Thu, 30 Nov 2017 13:38:12 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        kernel test robot <xiaolong.ye@...el.com>,
        Fengguang Wu <fengguang.wu@...el.com>
Subject: Re: [PATCH] x86/unwind_guess: Prevent using UNWINDER_GUESS=y with STACKDEPOT=y

On Thu, Nov 30, 2017 at 1:35 PM, Andrey Ryabinin
<aryabinin@...tuozzo.com> wrote:
> Stackdepot doesn't work well with CONFIG_UNWINDER_GUESS=y.
> The 'guess' unwinder generate awfully large and inaccurate stacktraces,
> thus stackdepot can't deduplicate stacktraces because they all look like
> unique. Eventually stackdepot reaches its capacity limit:
>
> WARNING: CPU: 0 PID: 545 at lib/stackdepot.c:119 depot_save_stack+0x28e/0x550
> Call Trace:
>  ? kasan_kmalloc+0x144/0x160
>  ? depot_save_stack+0x1f5/0x550
>  ? do_raw_spin_unlock+0xda/0xf0
>  ? preempt_count_sub+0x13/0xc0
>
> <...90 lines...>
>
>  ? do_raw_spin_unlock+0xda/0xf0
>
> Add STACKDEPOT=n dependency to UNWINDER_GUESS to avoid the problem.
>
> Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Reported-by: kernel test robot <xiaolong.ye@...el.com>
> Reported-by: Fengguang Wu <fengguang.wu@...el.com>
> ---
>  arch/x86/Kconfig.debug | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> index 6293a8768a91..672441c008c7 100644
> --- a/arch/x86/Kconfig.debug
> +++ b/arch/x86/Kconfig.debug
> @@ -400,6 +400,7 @@ config UNWINDER_FRAME_POINTER
>  config UNWINDER_GUESS
>         bool "Guess unwinder"
>         depends on EXPERT
> +       depends on !STACKDEPOT
>         ---help---
>           This option enables the "guess" unwinder for unwinding kernel stack
>           traces.  It scans the stack and reports every kernel text address it
> --
> 2.13.6
>


Acked-by: Dmitry Vyukov <dvyukov@...gle.com>