linux-kernel - Re: [PATCH 17/30] tracing: Improve panic/die notifiers

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Message-ID: <b8771b37-01f5-f50b-dbb3-9db4ee26e67e@gmail.com>
Date:   Fri, 29 Apr 2022 12:22:44 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...il.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org
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Subject: Re: [PATCH 17/30] tracing: Improve panic/die notifiers

Hello!

On 4/28/22 1:49 AM, Guilherme G. Piccoli wrote:

> Currently the tracing dump_on_oops feature is implemented
> through separate notifiers, one for die/oops and the other
> for panic. With the addition of panic notifier "id", this
> patch makes use of such "id" to unify both functions.
> 
> It also comments the function and changes the priority of the
> notifier blocks, in order they run early compared to other
> notifiers, to prevent useless trace data (like the callback
> names for the other notifiers). Finally, we also removed an
> unnecessary header inclusion.
> 
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
> ---
>  kernel/trace/trace.c | 57 +++++++++++++++++++++++++-------------------
>  1 file changed, 32 insertions(+), 25 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index f4de111fa18f..c1d8a3622ccc 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
[...]
> @@ -9767,38 +9766,46 @@ static __init int tracer_init_tracefs(void)
>  
>  fs_initcall(tracer_init_tracefs);
>  
> -static int trace_panic_handler(struct notifier_block *this,
> -			       unsigned long event, void *unused)
> +/*
> + * The idea is to execute the following die/panic callback early, in order
> + * to avoid showing irrelevant information in the trace (like other panic
> + * notifier functions); we are the 2nd to run, after hung_task/rcu_stall
> + * warnings get disabled (to prevent potential log flooding).
> + */
> +static int trace_die_panic_handler(struct notifier_block *self,
> +				unsigned long ev, void *unused)
>  {
> -	if (ftrace_dump_on_oops)
> +	int do_dump;

   bool?

> +
> +	if (!ftrace_dump_on_oops)
> +		return NOTIFY_DONE;
> +
> +	switch (ev) {
> +	case DIE_OOPS:
> +		do_dump = 1;
> +		break;
> +	case PANIC_NOTIFIER:
> +		do_dump = 1;
> +		break;

   Why not:

	case DIE_OOPS:
	case PANIC_NOTIFIER:
		do_dump = 1;
		break;

> +	default:
> +		do_dump = 0;
> +		break;
> +	}
> +
> +	if (do_dump)
>  		ftrace_dump(ftrace_dump_on_oops);
> -	return NOTIFY_OK;
> +
> +	return NOTIFY_DONE;
>  }
[...]

MBR, Sergey