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

From: Mathieu Desnoyers
Date: Mon Oct 07 2024 - 09:25:07 EST


On 2024-10-07 12:42, Peter Zijlstra wrote:
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.

I'll use this instead, thanks!

Mathieu


--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com