Re: [PATCH 2/4] irq_work: Fix irq_work_claim() ordering

Ingo Molnar
2019-11-11T07:20:14Z

* Frederic Weisbecker <frederic@kernel.org> wrote:

> When irq_work_claim() finds IRQ_WORK_PENDING flag already set, we just
> return and don't raise a new IPI. We expect the destination to see
> and handle our latest updades thanks to the pairing atomic_xchg()
> in irq_work_run_list().
>
> But cmpxchg() doesn't guarantee a full memory barrier upon failure. So
> it's possible that the destination misses our latest updates.
>
> So use atomic_fetch_or() instead that is unconditionally fully ordered
> and also performs exactly what we want here and simplify the code.

Just curious, how was this bug found - in the wild, or via code review?

Thanks,

Ingo