From b6fa08bc7bca48e0098b555e3c433e0969f46d4c Mon Sep 17 00:00:00 2001
From: Olivier Houchard <cognet@ci0.org>
Date: Sat, 1 Feb 2020 17:37:22 +0100
Subject: [PATCH] BUG/MEDIUM: memory_pool: Update the seq number in
 pool_flush().

In pool_flush(), we can't just set the free_list to NULL, or we may suffer
the ABA problem. Instead, use a double-width CAS and update the sequence
number.

This should be backported to 2.1, 2.0 and 1.9.
This may, or may not, be related to github issue #476.
---
 src/memory.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/memory.c b/src/memory.c
index a858a0983..24d709f1d 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -217,15 +217,20 @@ void *pool_refill_alloc(struct pool_head *pool, unsigned int avail)
  */
 void pool_flush(struct pool_head *pool)
 {
+	struct pool_free_list cmp, new;
 	void **next, *temp;
 	int removed = 0;
 
 	if (!pool)
 		return;
 	do {
-		next = pool->free_list;
-	} while (!_HA_ATOMIC_CAS(&pool->free_list, &next, NULL));
+		cmp.free_list = pool->free_list;
+		cmp.seq = pool->seq;
+		new.free_list = NULL;
+		new.seq = cmp.seq + 1;
+	} while (!_HA_ATOMIC_DWCAS(&pool->free_list, &cmp, &new));
 	__ha_barrier_atomic_store();
+	next = cmp.free_list;
 	while (next) {
 		temp = next;
 		next = *POOL_LINK(pool, temp);