linux-kernel - Re: [PATCH -next v2] ftrace: Fix potential warning in trace_printk_seq during ftrace

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Message-ID: <20250821110503.5f5c3156@gandalf.local.home>
Date: Thu, 21 Aug 2025 11:05:03 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Tengda Wu <wutengda@...weicloud.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Ingo Molnar <mingo@...e.hu>, linux-trace-kernel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v2] ftrace: Fix potential warning in
 trace_printk_seq during ftrace_dump

On Thu, 21 Aug 2025 02:11:20 +0000
Tengda Wu <wutengda@...weicloud.com> wrote:

 tested this and was writing the change log for the pull request when I
realized an issue.

> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 4283ed4e8f59..b4cec22753ea 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -10617,6 +10617,7 @@ static void ftrace_dump_one(struct trace_array *tr, enum ftrace_dump_mode dump_m
>  	 */
>  
>  	while (!trace_empty(&iter)) {
> +		void *ent;
>  
>  		if (!cnt)
>  			printk(KERN_TRACE "---------------------------------\n");
> @@ -10625,17 +10626,18 @@ static void ftrace_dump_one(struct trace_array *tr, enum ftrace_dump_mode dump_m
>  
>  		trace_iterator_reset(&iter);
>  		iter.iter_flags |= TRACE_FILE_LAT_FMT;
> +		ent = trace_find_next_entry_inc(&iter);
>  
> -		if (trace_find_next_entry_inc(&iter) != NULL) {
> +		if (ent) {

Why do we need "ent"?


>  			int ret;
>  
>  			ret = print_trace_line(&iter);
>  			if (ret != TRACE_TYPE_NO_CONSUME)
>  				trace_consume(&iter);
> +
> +			trace_printk_seq(&iter.seq);

Isn't just moving trace_printk_seq() enough?

The code is no different with or without the "ent" as "ent" is not used in
the if block.

-- Steve


>  		}
>  		touch_nmi_watchdog();
> -
> -		trace_printk_seq(&iter.seq);
>  	}
>  
>  	if (!cnt)