linux-kernel - Re: [PATCH v2] xtensa: improve stack dumping

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Date:   Tue, 12 Nov 2019 08:23:38 -0800
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>, Chris Zankel <chris@...kel.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <dima@...sta.com>, Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v2] xtensa: improve stack dumping

On Tue, Nov 12, 2019 at 1:49 AM Petr Mladek <pmladek@...e.com> wrote:
>
> On Thu 2019-11-07 16:44:48, Max Filippov wrote:
> > Calculate printable stack size and use print_hex_dump instead of
> > opencoding it.
> > Make size of stack dump configurable.
> > Drop extra newline output in show_trace as its output format does not
> > depend on CONFIG_KALLSYMS.
>
> > diff --git a/arch/xtensa/Kconfig.debug b/arch/xtensa/Kconfig.debug
> > index 39de98e20018..83cc8d12fa0e 100644
> > --- a/arch/xtensa/Kconfig.debug
> > +++ b/arch/xtensa/Kconfig.debug
> > @@ -31,3 +31,10 @@ config S32C1I_SELFTEST
> >         It is easy to make wrong hardware configuration, this test should catch it early.
> >
> >         Say 'N' on stable hardware.
> > +
> > +config PRINT_STACK_DEPTH
> > +     int "Stack depth to print" if DEBUG_KERNEL
> > +     default 64
> > +     help
> > +       This option allows you to set the stack depth that the kernel
> > +       prints in stack traces.
>
> I would split this into separate patch.

Sure, I'll split it out.

> > diff --git a/arch/xtensa/kernel/traps.c b/arch/xtensa/kernel/traps.c
> > index 4a6c495ce9b6..fe090ab1cab8 100644
> > --- a/arch/xtensa/kernel/traps.c
> > +++ b/arch/xtensa/kernel/traps.c
> > @@ -491,32 +491,24 @@ void show_trace(struct task_struct *task, unsigned long *sp)
> >
> >       pr_info("Call Trace:\n");
> >       walk_stackframe(sp, show_trace_cb, NULL);
> > -#ifndef CONFIG_KALLSYMS
> > -     pr_cont("\n");
> > -#endif
> >  }
> >
> > -static int kstack_depth_to_print = 24;
> > +static int kstack_depth_to_print = CONFIG_PRINT_STACK_DEPTH;
> >
> >  void show_stack(struct task_struct *task, unsigned long *sp)
> >  {
> > -     int i = 0;
> > -     unsigned long *stack;
> > +     size_t len;
> >
> >       if (!sp)
> >               sp = stack_pointer(task);
> > -     stack = sp;
> >
> > -     pr_info("Stack:\n");
> > +     len = min((-(unsigned long)sp) & (THREAD_SIZE - 4),
> > +               kstack_depth_to_print * 4ul);
>
> I would replace the hardcoded 4 with sizeof(void *).

It's not necessarily pointers, more like register-wide entries
on the stack. Ok, I guess I'll give it a name.

> > -     for (i = 0; i < kstack_depth_to_print; i++) {
> > -             if (kstack_end(sp))
> > -                     break;
> > -             pr_cont(" %08lx", *sp++);
> > -             if (i % 8 == 7)
> > -                     pr_cont("\n");
> > -     }
> > -     show_trace(task, stack);
> > +     pr_info("Stack:\n");
> > +     print_hex_dump(KERN_INFO, " ", DUMP_PREFIX_NONE, 32, 4,
> > +                    sp, len, false);
> > +     show_trace(task, sp);
> >  }
>
> The conversion looks fine to me. It is up to you (as a maintainer)
> what you do with the above proposal for two cosmetic changes ;-)
> Either way, feel free to use:
>
> Reviewed-by: Petr Mladek <pmladek@...e.com>

Thanks for the review.

-- Max