From: Willy Tarreau <w@1wt.eu>
Date: Fri, 28 Jul 2023 14:03:27 +0000 (+0000)
Subject: MEDIUM: peers: drop then re-acquire the wrlock in peer_send_teachmsgs()
X-Git-Tag: v2.9-dev3~21
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d4f8286e45618fa1017c79e32950487f1d1ad4d4;p=thirdparty%2Fhaproxy.git

MEDIUM: peers: drop then re-acquire the wrlock in peer_send_teachmsgs()

This function maintains the write lock for a while. In practice it does
not need to hold it that long, and some parts could be performed under a
read lock. This patch first drops then re-acquires the write lock at the
function's entry. The purpose is simply to break the end-to-end atomicity
to prove that it has no impact in case something needs to be bisected
later. In fact the write lock is already dropped while calling
peer_send_updatemsg().
---

diff --git a/src/peers.c b/src/peers.c
index c7c28b1ee0..23f6e5d12b 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -1575,8 +1575,10 @@ static inline int peer_send_teachmsgs(struct appctx *appctx, struct peer *p,
 	/* We force new pushed to 1 to force identifier in update message */
 	new_pushed = 1;
 
-	if (!locked)
-		HA_RWLOCK_WRLOCK(STK_TABLE_LOCK, &st->table->lock);
+	if (locked)
+		HA_RWLOCK_WRUNLOCK(STK_TABLE_LOCK, &st->table->lock);
+
+	HA_RWLOCK_WRLOCK(STK_TABLE_LOCK, &st->table->lock);
 
 	while (1) {
 		struct stksess *ts;
@@ -1633,8 +1635,10 @@ static inline int peer_send_teachmsgs(struct appctx *appctx, struct peer *p,
 	}
 
  out:
-	if (!locked)
-		HA_RWLOCK_WRUNLOCK(STK_TABLE_LOCK, &st->table->lock);
+	HA_RWLOCK_WRUNLOCK(STK_TABLE_LOCK, &st->table->lock);
+
+	if (locked)
+		HA_RWLOCK_WRLOCK(STK_TABLE_LOCK, &st->table->lock);
 	return ret;
 }