Re: [PATCH v4 02/39] task_work: Fix TWA_NMI_CURRENT race with __schedule()

Josh Poimboeuf
2025-04-22T17:20:10Z

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@infradead.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