linux-kernel - Re: [PATCH] kernel/trace: Fix cleanup logic of enable_trace

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Message-ID: <20230628084428.7bb32d65@rorschach.local.home>
Date:   Wed, 28 Jun 2023 08:44:28 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@...il.com>
Cc:     mhiramat@...nel.org, dan.carpenter@...aro.org,
        linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/trace: Fix cleanup logic of enable_trace_eprobe

On Wed, 28 Jun 2023 15:18:11 +0300
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@...il.com> wrote:

> The enable_trace_eprobe() function enables all event probes, attached
> to given trace probe. If an error occurs in enabling one of the event
> probes, all others should be roll backed. There is a bug in that roll
> back logic - instead of all event probes, only the failed one is
> disabled.
> 
> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> Fixes: 7491e2c44278 ("tracing: Add a probe that attaches to trace events")
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@...il.com>
> ---
>  kernel/trace/trace_eprobe.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
> index 67e854979d53..ba9a28bc773f 100644
> --- a/kernel/trace/trace_eprobe.c
> +++ b/kernel/trace/trace_eprobe.c
> @@ -702,8 +702,12 @@ static int enable_trace_eprobe(struct trace_event_call *call,
>  
>  	if (ret) {
>  		/* Failed to enable one of them. Roll back all */
> -		if (enabled)
> -			disable_eprobe(ep, file->tr);
> +		if (enabled) {

If one was enabled and the second one failed, that should only happen
if there's a bug in the kernel (unless the failure was due to a memory
problem).

I wonder if we should add:

			int cnt = 0;

> +			list_for_each_entry(pos, trace_probe_probe_list(tp), list) {

				/*
				 * It's a bug if one failed for something other than memory
				 * not being available but another eprobe succeeded.
				 */
				WARN_ON_ONCE(cnt++ && ret != -ENOMEM);

-- Steve


> +				ep = container_of(pos, struct trace_eprobe, tp);
> +				disable_eprobe(ep, file->tr);
> +			}
> +		}
>  		if (file)
>  			trace_probe_remove_file(tp, file);
>  		else