linux-kernel - Re: [PATCH] print kdump kernel loaded status in stack dump

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Date:   Fri, 26 Jan 2018 13:17:57 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Andi Kleen <ak@...ux.intel.com>, sergey.senozhatsky@...il.com,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH] print kdump kernel loaded status in stack dump

On Fri 2018-01-26 15:37:24, Dave Young wrote:
> On 01/19/18 at 12:47pm, Dave Young wrote:
> > On 01/18/18 at 01:57pm, Steven Rostedt wrote:
> > > On Thu, 18 Jan 2018 10:02:17 -0800
> > > Andi Kleen <ak@...ux.intel.com> wrote:
> > > 
> > > > Dave Young <dyoung@...hat.com> writes:
> > > > >  		printk("%sHardware name: %s\n",
> > > > >  		       log_lvl, dump_stack_arch_desc_str);
> > > > > +	if (kexec_crash_loaded())
> > > > > +		printk("%skdump kernel loaded\n", log_lvl);  
> > > > 
> > > > Oops/warnings are getting longer and longer, often scrolling away
> > > > from the screen, and if the kernel crashes backscroll does not work
> > > > anymore, so precious information is lost.
> > > > 
> > > > Can you merge it with some other line?
> > > > 
> > > > Just a [KDUMP] or so somewhere should be good enough.
> > > 
> > > Or perhaps we should add it as a TAINT. Not all taints are bad.
> > 
> > Hmm, I also thought about this before but It sounds like not match the
> > "tainted" meaning with the assumption that it is bad :(
> > 
> > Maybe it would be better to do like Andi said, but print a better word
> > than "KDUMP", eg. "Kdumpable" sounds better.  If this is fine I can
> > repost the patch.
> 
> I have been not available recently, sorry for late about the update,
> rethinking about this, it is looks good to use "[KDUMP]".  Also for
> the tainted flags, I tried but it is not what we want since kdump kernel
> can be unloaded, this is not like "tainted" which can only be added and
> it can not be removed.
> 
> How about below version?
> ---
> 
> It is useful to print kdump kernel loaded status in dump_stack() 
> especially when panic happens so that we can  differentiate
> kdump kernel early hang and a normal panic in a bug report.
> 
> Signed-off-by: Dave Young <dyoung@...hat.com>
> ---
> [v1 -> v2] merge the status in other line as Andi Kleen suggested
>  kernel/printk/printk.c |    3 +++
> --- linux.orig/kernel/printk/printk.c
> +++ linux/kernel/printk/printk.c
> @@ -48,6 +48,7 @@
>  #include <linux/sched/clock.h>
>  #include <linux/sched/debug.h>
>  #include <linux/sched/task_stack.h>
> +#include <linux/kexec.h>
>  
>  #include <linux/uaccess.h>
>  #include <asm/sections.h>
> @@ -3118,9 +3119,11 @@ void __init dump_stack_set_arch_desc(con
>   */
>  void dump_stack_print_info(const char *log_lvl)
>  {
> -	printk("%sCPU: %d PID: %d Comm: %.20s %s %s %.*s\n",
> +	printk("%sCPU: %d PID: %d Comm: %.20s %s %s %s %.*s\n",
>  	       log_lvl, raw_smp_processor_id(), current->pid, current->comm,
> -	       print_tainted(), init_utsname()->release,
> +	       print_tainted(),
> +	       kexec_crash_loaded() ? "[KDUMP]" : "",

I am afraid that people might be confused what that exactly means.
For example, if I would wonder if it was already running the crashdump
kernel.

And two small nits. It always prints the extra space. It does not fit
the style of the line.

What about the following?

	printk("%sCPU: %d PID: %d Comm: %.20s %s%s %s %.*s\n",
	       log_lvl, raw_smp_processor_id(), current->pid, current->comm,
	       kexec_crash_loaded() ? "Kdump: loaded " : "",
	       print_tainted(),
	       init_utsname()->release,
	       (int)strcspn(init_utsname()->version, " "),
	       init_utsname()->version);

It would produce something like:

CPU: 0 PID: 0 Comm: swapper/0 Kdump: loaded Not tainted 4.14.0-4-default+ #670


Best Regards,
Petr