linux-kernel - Re: [PATCH 1/3] printk: Fix kdb_trap

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Date:   Tue, 3 Oct 2017 18:10:41 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     pmladek@...e.com, sergey.senozhatsky@...il.com,
        linux-kernel@...r.kernel.org, mingo@...nel.org, tglx@...utronix.de,
        Jason Wessel <jason.wessel@...driver.com>
Subject: Re: [PATCH 1/3] printk: Fix kdb_trap_printk placement

On Thu, 28 Sep 2017 14:18:24 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> Some people figured vprintk_emit() makes for a nice API and exported
> it, bypassing the kdb trap.
> 
> This still leaves vprintk_nmi() outside of the kbd reach, should that
> be fixed too?

I believe the vprintk_nmi() just buffers the prints, and doesn't send
it out. I'm guessing not then.

> 
> Cc: Jason Wessel <jason.wessel@...driver.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/printk/printk.c |   18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1811,6 +1811,11 @@ asmlinkage int vprintk_emit(int facility
>  	int printed_len;
>  	bool in_sched = false;
>  
> +#ifdef CONFIG_KGDB_KDB
> +	if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
> +		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
> +#endif
> +
>  	if (level == LOGLEVEL_SCHED) {
>  		level = LOGLEVEL_DEFAULT;
>  		in_sched = true;
> @@ -1903,18 +1908,7 @@ EXPORT_SYMBOL(printk_emit);
>  
>  int vprintk_default(const char *fmt, va_list args)
>  {
> -	int r;
> -
> -#ifdef CONFIG_KGDB_KDB
> -	/* Allow to pass printk() to kdb but avoid a recursion. */
> -	if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0)) {
> -		r = vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
> -		return r;
> -	}
> -#endif
> -	r = vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
> -
> -	return r;

Hmm, what was with the return r before??

Anyway,

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> +	return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
>  }
>  EXPORT_SYMBOL_GPL(vprintk_default);
>  
>