linux-kernel - Re: [PATCH] ftrace: Handle commands when closing set_ftrace

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Date:   Thu, 13 May 2021 22:24:19 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ftrace: Handle commands when closing set_ftrace_filter
 file

On Wed, May 05, 2021 at 10:48:18AM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
>  # echo switch_mm:traceoff > /sys/kernel/tracing/set_ftrace_filter
> 
> will cause switch_mm to stop tracing by the traceoff command.
> 
>  # echo -n switch_mm:traceoff > /sys/kernel/tracing/set_ftrace_filter
> 
> does nothing.
> 
> The reason is that the parsing in the write function only processes
> commands if it finished parsing (there is white space written after the
> command). That's to handle:
> 
>  write(fd, "switch_mm:", 10);
>  write(fd, "traceoff", 8);
> 
> cases, where the command is broken over multiple writes.
> 
> The problem is if the file descriptor is closed, then the write call is
> not processed, and the command needs to be processed in the release code.
> The release code can handle matching of functions, but does not handle
> commands.
> 
> Cc: stable@...r.kernel.org
> Fixes: eda1e32855656 ("tracing: handle broken names in ftrace filter")

nice, breaking kernel since 2009.. I'll put that on t-shirt ;-)

I saw the patch got already merged, FWIW:

Acked-by: Jiri Olsa <jolsa@...nel.org>

jirka

> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  kernel/trace/ftrace.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 057e962ca5ce..c57508445faa 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5591,7 +5591,10 @@ int ftrace_regex_release(struct inode *inode, struct file *file)
>  
>  	parser = &iter->parser;
>  	if (trace_parser_loaded(parser)) {
> -		ftrace_match_records(iter->hash, parser->buffer, parser->idx);
> +		int enable = !(iter->flags & FTRACE_ITER_NOTRACE);
> +
> +		ftrace_process_regex(iter, parser->buffer,
> +				     parser->idx, enable);
>  	}
>  
>  	trace_parser_put(parser);
> -- 
> 2.29.2
>