linux-kernel - Re: [PATCH] tracing: Do not synchronize freeing of trigger filter on boot up

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Message-Id: <20221214084954.e759647a2f5f1a38bc78b371@kernel.org>
Date:   Wed, 14 Dec 2022 08:49:54 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] tracing: Do not synchronize freeing of trigger filter
 on boot up

On Tue, 13 Dec 2022 17:24:29 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> If a trigger filter on the kernel command line fails to apply (due to
> syntax error), it will be freed. The freeing will call
> tracepoint_synchronize_unregister(), but this is not needed during early
> boot up, and will even trigger a lockdep splat.
> 
> Avoid calling the synchronization function when system_state is
> SYSTEM_BOOTING.

Shouldn't this be done inside tracepoint_synchronize_unregister()?
Then, it will prevent similar warnings if we expand boot time feature.

Thank you,

> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/trace_events_trigger.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
> index 19ce9d22bfd7..e535959939d3 100644
> --- a/kernel/trace/trace_events_trigger.c
> +++ b/kernel/trace/trace_events_trigger.c
> @@ -1085,8 +1085,14 @@ int set_trigger_filter(char *filter_str,
>  	rcu_assign_pointer(data->filter, filter);
>  
>  	if (tmp) {
> -		/* Make sure the call is done with the filter */
> -		tracepoint_synchronize_unregister();
> +		/*
> +		 * Make sure the call is done with the filter.
> +		 * It is possible that a filter could fail at boot up,
> +		 * and then this path will be called. Avoid the synchronization
> +		 * in that case.
> +		 */
> +		if (system_state != SYSTEM_BOOTING)
> +			tracepoint_synchronize_unregister();
>  		free_event_filter(tmp);
>  	}
>  
> -- 
> 2.35.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>