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());
+
+ if (!addr)
+ return;
+ /* Memory ordering: Store A before Load B. */
+ smp_mb();
+ /* Scan all CPUs slots. */
+ for_each_possible_cpu(cpu) {
+ struct hp_slot *slot = per_cpu_ptr(percpu_slots, cpu);
+
+ if (retire_cb && smp_load_acquire(&slot->addr) == addr) /* Load B */
+ retire_cb(cpu, slot, addr);
Is retirce_cb allowed to cmpxchg the thing?
Renaming retire_cb to "on_match_cb". Whatever the callback does needs to
be done with knowledge of the slot user (e.g. IPI).
+ /* Busy-wait if node is found. */
+ while ((smp_load_acquire(&slot->addr)) == addr) /* Load B */
+ cpu_relax();
This really should be using smp_cond_load_acquire()
Done,
Thanks,
Mathieu
+ }
+}
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
