Re: [RFC PATCH v2 3/4] hp: Implement Hazard Pointers

[Peter Zijlstra]

On Sat, Oct 05, 2024 at 02:56:26PM -0400, Mathieu Desnoyers wrote:
> On 2024-10-05 18:07, Peter Zijlstra wrote:
> > On Sat, Oct 05, 2024 at 06:04:44PM +0200, Peter Zijlstra wrote:
> > > On Fri, Oct 04, 2024 at 02:27:33PM -0400, Mathieu Desnoyers wrote:
> > 
> > > > +void hp_scan(struct hp_slot __percpu *percpu_slots, void *addr,
> > > > +	     void (*retire_cb)(int cpu, struct hp_slot *slot, void *addr))
> > > > +{
> > > > +	int cpu;
> > > > +
> > > > +	/*
> > > > +	 * Store A precedes hp_scan(): it unpublishes addr (sets it to
> > > > +	 * NULL or to a different value), and thus hides it from hazard
> > > > +	 * pointer readers.
> > > > +	 */
> > 
> > This should probably assert we're in a preemptible context. Otherwise
> > people will start using this in non-preemptible context and then we get
> > to unfuck things later.
> 
> Something like this ?
> 
> +       /* Should only be called from preemptible context. */
> +       WARN_ON_ONCE(in_atomic());

	lockdep_assert_preemption_enabled();

that also checks local IRQ state IIRC.