[PATCH 27/28] hazptr: Add Bloom false-positive exact-match fallback

[Kunwu Chan]

After 200+ scan cycles without progress, do an exact-match
per-address walk to determine whether the address is truly
present in any per-CPU or overflow-list slot.  If absent,
complete the waiter immediately.  A wildcard counts as present.

Signed-off-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>
---
 kernel/hazptr.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/hazptr.c b/kernel/hazptr.c
index 66954251c332..13ae9eb26a8b 100644
--- a/kernel/hazptr.c
+++ b/kernel/hazptr.c
@@ -407,6 +407,7 @@ struct hazptr_waiter {
 #endif
 #ifdef CONFIG_HAZPTR_DRAIN_ASSIST
 	unsigned int drain_cycles;
+	unsigned int bloom_cycles;	/* cycles since last exact match */
 #endif
 };
 
@@ -852,6 +853,18 @@ static void hazptr_scan_do_cycle(void)
 
 	mutex_unlock(&hazptr_phase_lock);
 
+	/* Bloom-false-positive fallback */
+	list_for_each_entry_safe(w, n, &hazptr_scan.scanning, node) {
+		w->bloom_cycles++;
+		if (w->bloom_cycles > 200) {
+			if (!hazptr_scan_walk(w->addr, NULL, NULL)) {
+				list_move(&w->node, &done);
+			} else {
+				w->bloom_cycles = 0;
+			}
+		}
+	}
+
 	list_for_each_entry_safe(w, n, &done, node) {
 		list_del_init(&w->node);
 		complete(&w->done);
-- 
2.43.0