linux-kernel - Re: [PATCH v2] panic: add an option to replay all the printk message in buffer

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Message-ID: <20190418090044.wqpc7wooboamvl6t@shbuild888>
Date:   Thu, 18 Apr 2019 17:00:44 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Borislav Petkov <bp@...e.de>, ying.huang@...el.com
Subject: Re: [PATCH v2] panic: add an option to replay all the printk message
 in buffer

Hi Petr,

On Thu, Apr 18, 2019 at 09:45:52AM +0200, Petr Mladek wrote:
> On Thu 2019-04-18 09:00:14, Sergey Senozhatsky wrote:
> > I think that PANIC_PRINT_ALL_PRINTK_MSG is a debugging option; a quite
> > specific one. So people who ask the kernel to PANIC_PRINT_ALL_PRINTK_MSG
> > they know what they are doing, and we probably will not cofuse anyone.
> > After all, we don't print any headers when we ftrace_dump() or imitate
> > sysrq via sysrq_timer_list_show(), or for any other panic_print_sys_info()
> > printouts. So it's OK to just do the simple thing for
> > PANIC_PRINT_ALL_PRINTK_MSG.
> 
> The following functions are currently called from panic_print_sys_info():
> 
> + show_state():
> 	printk(KERN_INFO
> 		"  task                        PC stack   pid father\n");
> + show_mem():
> 	printk("Mem-Info:\n");
> 
> + sysrq_timer_list_show()
> 	no global header; but each section can be easily distinguished
> 	because there are several static strings that explains the
> 	content
> 
> + debug_show_all_locks()
> 	pr_warn("\nShowing all locks held in the system:\n");
> 
> + ftrace_dump():
> 	printk(KERN_TRACE "Dumping ftrace buffer:\n");
> 
> 
> The person that enabled the debugging option might know what it did
> when it process the log the very same day. It might be less clear
> for others reading the log.
> 
> Also it still might be convenient to find the beginning easily.
> Or it might help to orientate when several test runs
> (over night test) are squashed in a single file. I see
> such logs pretty often.

Thanks for checking all the info. For the note, how about adding
something like this inside panic_print_sys_info()?

	if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG) {
		printk("\nprintk: will replay all the messages in buffer:\n");
		console_flush_on_panic(CONSOLE_FLUSH_ALL);
	}

If you are all fine with it, I'll go post a v3, thanks,

- Feng

> 
> That said, I do not resist on it.
> 
> Best Regards,
> Petr