Message-ID: <YqG6URbihTNCk9YR@alley>
Date:   Thu, 9 Jun 2022 11:16:46 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
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Subject: Re: [PATCH 24/36] printk: Remove trace_.*_rcuidle() usage

On Wed 2022-06-08 16:27:47, Peter Zijlstra wrote:
> The problem, per commit fc98c3c8c9dc ("printk: use rcuidle console
> tracepoint"), was printk usage from the cpuidle path where RCU was
> already disabled.
> 
> Per the patches earlier in this series, this is no longer the case.

My understanding is that this series reduces a lot the amount
of code called with RCU disabled. As a result the particular printk()
call mentioned by commit fc98c3c8c9dc ("printk: use rcuidle console
tracepoint") is called with RCU enabled now. Hence this particular
problem is fixed better way now.

But is this true in general?
Does this "prevent" calling printk() a safe way in code with
RCU disabled?

I am not sure if anyone cares. printk() is the best effort
functionality because of the consoles code anyway. Also I wonder
if anyone uses this trace_console().

Therefore if this patch allows to remove some tricky tracing
code then it might be worth it. But if trace_console_rcuidle()
variant is still going to be available then I would keep using it.

Best Regards,
Petr

> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/printk/printk.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2238,7 +2238,7 @@ static u16 printk_sprint(char *text, u16
>  		}
>  	}
>  
> -	trace_console_rcuidle(text, text_len);
> +	trace_console(text, text_len);
>  
>  	return text_len;
>  }
> 

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