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 <[email protected]> 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