[PATCH v2] xtensa: improve stack dumping

[PATCH v2] xtensa: improve stack dumping

[Max Filippov]

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.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
Changes v1->v2:
- use print_hex_dump.

 arch/xtensa/Kconfig.debug  |  7 +++++++
 arch/xtensa/kernel/traps.c | 24 ++++++++----------------
 2 files changed, 15 insertions(+), 16 deletions(-)

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.
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);
 
-	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);
 }
 
 DEFINE_SPINLOCK(die_lock);
-- 
2.20.1

Re: [PATCH v2] xtensa: improve stack dumping

[Petr Mladek]

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.

> 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 *).

>  
> -	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@suse.com>

Best Regards,
Petr

Re: [PATCH v2] xtensa: improve stack dumping

[Max Filippov]

On Tue, Nov 12, 2019 at 1:49 AM Petr Mladek <pmladek@suse.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@suse.com>

Thanks for the review.

-- Max