linux-kernel - Re: [PATCH v4 02/39] task_work: Fix TWA_NMI_CURRENT race with _

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Message-ID: <37bx6zbikhhxehbch6yi7urc2g2uwxrl4lktexl35zubo5xm6z@xf5o3srbjx7v>
Date: Tue, 22 Apr 2025 10:20:07 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, 
	Ingo Molnar <mingo@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, 
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>, 
	Mark Rutland <mark.rutland@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>, 
	linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>, Sam James <sam@...too.org>, 
	linux-trace-kernel@...r.kernel.org, Andrii Nakryiko <andrii.nakryiko@...il.com>, 
	Jens Remus <jremus@...ux.ibm.com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Florian Weimer <fweimer@...hat.com>, Andy Lutomirski <luto@...nel.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Weinan Liu <wnliu@...gle.com>
Subject: Re: [PATCH v4 02/39] task_work: Fix TWA_NMI_CURRENT race with
 __schedule()

On Tue, Apr 22, 2025 at 12:15:41PM -0400, Steven Rostedt wrote:
> On Wed, 22 Jan 2025 13:42:28 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > If we hit before schedule(), all just works as expected, if we hit after
> > schedule(), the task will already have the TIF flag set, and we'll hit
> > the return to user path once it gets scheduled again.
> > 
> > ---
> > diff --git a/kernel/task_work.c b/kernel/task_work.c
> > index c969f1f26be5..155549c017b2 100644
> > --- a/kernel/task_work.c
> > +++ b/kernel/task_work.c
> > @@ -9,7 +9,12 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */
> >  #ifdef CONFIG_IRQ_WORK
> >  static void task_work_set_notify_irq(struct irq_work *entry)
> >  {
> > -	test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
> > +	/*
> > +	 * no-op IPI
> > +	 *
> > +	 * TWA_NMI_CURRENT will already have set the TIF flag, all
> > +	 * this interrupt does it tickle the return-to-user path.
> > +	 */
> >  }
> >  static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =
> >  	IRQ_WORK_INIT_HARD(task_work_set_notify_irq);
> > @@ -98,6 +103,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
> >  		break;
> >  #ifdef CONFIG_IRQ_WORK
> >  	case TWA_NMI_CURRENT:
> > +		set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
> >  		irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
> >  		break;
> >  #endif
> 
> Does this patch replace patches 1 and 2?

Indeed it does.

> If so, Peter, can you give me a Signed-off-by?
> 
> -- Steve

-- 
Josh