linux-kernel - Re: [PATCH v8 24/37] tracing: Add support for 'synthetic' events

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180110054124.GA2575@danjae.aot.lge.com>
Date:   Wed, 10 Jan 2018 14:41:24 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, mhiramat@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel.opensrc@...il.com, joelaf@...gle.com,
        mathieu.desnoyers@...icios.com, baohong.liu@...el.com,
        rajvi.jingar@...el.com, julia@...com, fengguang.wu@...el.com,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        kernel-team@....com
Subject: Re: [PATCH v8 24/37] tracing: Add support for 'synthetic' events

Hi Tom,

On Thu, Dec 21, 2017 at 10:02:46AM -0600, Tom Zanussi wrote:
> Synthetic events are user-defined events generated from hist trigger
> variables saved from one or more other events.
> 
> To define a synthetic event, the user writes a simple specification
> consisting of the name of the new event along with one or more
> variables and their type(s), to the tracing/synthetic_events file.
> 
> For instance, the following creates a new event named 'wakeup_latency'
> with 3 fields: lat, pid, and prio:
> 
>     # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \
>       /sys/kernel/debug/tracing/synthetic_events
> 
> Reading the tracing/synthetic_events file lists all the
> currently-defined synthetic events, in this case the event we defined
> above:
> 
>     # cat /sys/kernel/debug/tracing/synthetic_events
>     wakeup_latency u64 lat; pid_t pid; int prio
> 
> At this point, the synthetic event is ready to use, and a histogram
> can be defined using it:
> 
>     # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \
>     /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
> 
> The new event is created under the tracing/events/synthetic/ directory
> and looks and behaves just like any other event:
> 
>     # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency
>       enable  filter  format  hist  id  trigger
> 
> Although a histogram can be defined for it, nothing will happen until
> an action tracing that event via the trace_synth() function occurs.
> The trace_synth() function is very similar to all the other trace_*
> invocations spread throughout the kernel, except in this case the
> trace_ function and its corresponding tracepoint isn't statically
> generated but defined by the user at run-time.
> 
> How this can be automatically hooked up via a hist trigger 'action' is
> discussed in a subsequent patch.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> [fix noderef.cocci warnings, sizeof pointer for kcalloc of event->fields]
> Signed-off-by: Fengguang Wu <fengguang.wu@...el.com>
> ---

[SNIP]
> +static int release_all_synth_events(void)
> +{
> +	struct list_head release_events;
> +	struct synth_event *event, *e;
> +	int ret = 0, err = 0;
> +
> +	INIT_LIST_HEAD(&release_events);
> +
> +	mutex_lock(&synth_event_mutex);
> +
> +	list_for_each_entry(event, &synth_event_list, list) {
> +		if (event->ref) {
> +			mutex_unlock(&synth_event_mutex);
> +			return -EBUSY;
> +		}
> +	}
> +
> +	list_for_each_entry_safe(event, e, &synth_event_list, list)
> +		list_move(&event->list, &release_events);

list_splice_init() ?

> +
> +	mutex_unlock(&synth_event_mutex);
> +
> +	list_for_each_entry_safe(event, e, &release_events, list) {
> +		list_del(&event->list);
> +
> +		ret = unregister_synth_event(event);
> +		add_or_delete_synth_event(event, !ret);
> +	}
> +
> +	if (err)
> +		ret = err;

The err was never used.

> +
> +	return ret;
> +}