From: Willy Tarreau <w@1wt.eu>
Date: Thu, 24 Jun 2021 05:22:03 +0000 (+0200)
Subject: Revert "MEDIUM: queue: move the queue lock manipulation to pendconn_process_next_strm()"
X-Git-Tag: v2.5-dev1~40
X-Git-Url: http://git.haproxy.org/?a=commitdiff_plain;h=5343d8ed6f0e8129ed51234918f75d5b3c3a2610;p=haproxy-2.5.git

Revert "MEDIUM: queue: move the queue lock manipulation to pendconn_process_next_strm()"

This reverts commit 9a6d0ddbd6788a05c6730bf0e9e8550d7c5b11aa.

The recent changes since 5304669e1 MEDIUM: queue: make
pendconn_process_next_strm() only return the pendconn opened a tiny race
condition between stream_free() and process_srv_queue(), as the pendconn
is accessed outside of the lock, possibly while it's being freed. A
different approach is required.
---

diff --git a/src/queue.c b/src/queue.c
index 8db2da2..5c9db17 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -255,8 +255,8 @@ static struct pendconn *pendconn_first(struct eb_root *pendconns)
  *
  * The proxy's queue will be consulted only if px_ok is non-zero.
  *
- * This function uses both the proxy and the server queues' lock. Today it is
- * only called by process_srv_queue.
+ * This function must only be called if the server queue _AND_ the proxy queue
+ * are locked (if pk_ok is set). Today it is only called by process_srv_queue.
  *
  * The function returns the dequeued pendconn on success or NULL if none is
  * available. It's up to the caller to add the corresponding stream to the
@@ -270,20 +270,15 @@ static struct pendconn *pendconn_process_next_strm(struct server *srv, struct pr
 	u32 pkey, ppkey;
 
 	p = NULL;
-	HA_SPIN_LOCK(QUEUE_LOCK, &srv->queue.lock);
 	if (srv->queue.length)
 		p = pendconn_first(&srv->queue.head);
 
 	pp = NULL;
-	HA_SPIN_LOCK(QUEUE_LOCK, &px->queue.lock);
 	if (px_ok && px->queue.length)
 		pp = pendconn_first(&px->queue.head);
 
-	if (!p && !pp) {
-		HA_SPIN_UNLOCK(QUEUE_LOCK, &px->queue.lock);
-		HA_SPIN_UNLOCK(QUEUE_LOCK, &srv->queue.lock);
+	if (!p && !pp)
 		return NULL;
-	}
 	else if (!pp)
 		goto use_p; /*  p != NULL */
 	else if (!p)
@@ -312,17 +307,13 @@ static struct pendconn *pendconn_process_next_strm(struct server *srv, struct pr
  use_pp:
 	/* Let's switch from the server pendconn to the proxy pendconn */
 	__pendconn_unlink_prx(pp);
-	HA_SPIN_UNLOCK(QUEUE_LOCK, &px->queue.lock);
-	HA_SPIN_UNLOCK(QUEUE_LOCK, &srv->queue.lock);
 	_HA_ATOMIC_INC(&px->queue.idx);
 	_HA_ATOMIC_DEC(&px->queue.length);
 	_HA_ATOMIC_DEC(&px->totpend);
 	p = pp;
 	goto unlinked;
  use_p:
-	HA_SPIN_UNLOCK(QUEUE_LOCK, &px->queue.lock);
 	__pendconn_unlink_srv(p);
-	HA_SPIN_UNLOCK(QUEUE_LOCK, &srv->queue.lock);
 	_HA_ATOMIC_INC(&srv->queue.idx);
 	_HA_ATOMIC_DEC(&srv->queue.length);
 	_HA_ATOMIC_DEC(&px->totpend);
@@ -356,8 +347,14 @@ void process_srv_queue(struct server *s)
 	while (s->served < maxconn) {
 		struct pendconn *pc;
 
+		HA_SPIN_LOCK(QUEUE_LOCK, &s->queue.lock);
+		HA_SPIN_LOCK(QUEUE_LOCK, &p->queue.lock);
+
 		pc = pendconn_process_next_strm(s, p, px_ok);
 
+		HA_SPIN_UNLOCK(QUEUE_LOCK, &p->queue.lock);
+		HA_SPIN_UNLOCK(QUEUE_LOCK, &s->queue.lock);
+
 		if (!pc)
 			break;