linux-kernel - Re: [PATCH v4 2/6] perf: Enqueue SIGTRAP always via task

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Message-ID: <20240701132725.9_UHcpVA@linutronix.de>
Date: Mon, 1 Jul 2024 15:27:25 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Daniel Bristot de Oliveira <bristot@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Ian Rogers <irogers@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>, Kan Liang <kan.liang@...ux.intel.com>,
	Marco Elver <elver@...gle.com>, Mark Rutland <mark.rutland@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH v4 2/6] perf: Enqueue SIGTRAP always via task_work.

On 2024-07-01 14:28:29 [+0200], Peter Zijlstra wrote:
> On Mon, Jun 24, 2024 at 05:15:15PM +0200, Sebastian Andrzej Siewior wrote:
> > @@ -9735,18 +9719,28 @@ static int __perf_event_overflow(struct perf_event *event,
> >  
> >  		if (regs)
> >  			pending_id = hash32_ptr((void *)instruction_pointer(regs)) ?: 1;
> > -		if (!event->pending_sigtrap) {
> > -			event->pending_sigtrap = pending_id;
> > +
> > +		if (!event->pending_work &&
> > +		    !task_work_add(current, &event->pending_task, TWA_RESUME)) {
> > +			event->pending_work = pending_id;
> >  			local_inc(&event->ctx->nr_pending);
> 
> task_work_add() isn't NMI safe, at the very least the
> kasan_record_aux_stack() thing needs to go. But the whole
> set_notify_resume() thing also needs an audit.

oh. I just peeked and set_notify_resume() wouldn't survive the audit.
Would you mind adding task_work_add_nmi() which is task_work_add(,
TWA_NONE) without kasan_record_aux_stack()? The signal part would need
to be moved the irq_work() below in the NMI case.

Sebastian