linux-kernel - Re: [PATCHv2 47/50] kdb: Don't play with console

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Date:   Tue, 17 Mar 2020 16:00:49 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Douglas Anderson <dianders@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net
Subject: Re: [PATCHv2 47/50] kdb: Don't play with console_loglevel

On Mon, Mar 16, 2020 at 02:39:13PM +0000, Dmitry Safonov wrote:
> Print the stack trace with KERN_EMERG - it should be always visible.
> 
> Playing with console_loglevel is a bad idea as there may be more
> messages printed than wanted. Also the stack trace might be not printed
> at all if printk() was deferred and console_loglevel was raised back
> before the trace got flushed.
> 
> Unfortunately, after rebasing on commit 2277b492582d ("kdb: Fix stack
> crawling on 'running' CPUs that aren't the master"), kdb_show_stack()
> uses now kdb_dump_stack_on_cpu(), which for now won't be converted as it
> uses dump_stack() instead of show_stack().
> 
> Convert for now the branch that uses show_stack() and remove
> console_loglevel exercise from that case.
> 
> Cc: Daniel Thompson <daniel.thompson@...aro.org>
> Cc: Douglas Anderson <dianders@...omium.org>
> Cc: Jason Wessel <jason.wessel@...driver.com>
> Cc: kgdb-bugreport@...ts.sourceforge.net
> Signed-off-by: Dmitry Safonov <dima@...sta.com>

Acked-by: Daniel Thompson <daniel.thompson@...aro.org>


> ---
>  kernel/debug/kdb/kdb_bt.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
> index 3de0cc780c16..43f5dcd2b9ac 100644
> --- a/kernel/debug/kdb/kdb_bt.c
> +++ b/kernel/debug/kdb/kdb_bt.c
> @@ -21,17 +21,18 @@
>  
>  static void kdb_show_stack(struct task_struct *p, void *addr)
>  {
> -	int old_lvl = console_loglevel;
> -
> -	console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
>  	kdb_trap_printk++;
>  
> -	if (!addr && kdb_task_has_cpu(p))
> +	if (!addr && kdb_task_has_cpu(p)) {
> +		int old_lvl = console_loglevel;
> +
> +		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
>  		kdb_dump_stack_on_cpu(kdb_process_cpu(p));
> -	else
> -		show_stack(p, addr);
> +		console_loglevel = old_lvl;
> +	} else {
> +		show_stack_loglvl(p, addr, KERN_EMERG);
> +	}
>  
> -	console_loglevel = old_lvl;
>  	kdb_trap_printk--;
>  }
>  
> -- 
> 2.25.1
>