BUG/MAJOR: server: fix deadlock when changing maxconn via agent-check
The server_parse_maxconn_change_request locks the server lock. However,
this function can be called via agent-checks or lua code which already
lock it. This bug has been introduced by the following commit :
commit 79a88ba3d09f7e2b73ae27cb5d24cc087a548fa6
BUG/MAJOR: server: prevent deadlock when using 'set maxconn server'
This commit tried to fix another deadlock with can occur because
previoulsy server_parse_maxconn_change_request requires the server lock
to be held. However, it may call internally process_srv_queue which also
locks the server lock. The locking policy has thus been updated. The fix
is functional for the CLI 'set maxconn' but fails to address the
agent-check / lua counterparts.
This new issue is fixed in two steps :
- changes from the above commit have been reverted. This means that
server_parse_maxconn_change_request must again be called with the
server lock.
- to counter the deadlock fixed by the above commit, process_srv_queue
now takes an argument to render the server locking optional if the
caller already held it. This is only used by
server_parse_maxconn_change_request.
The above commit was subject to backport up to 1.8. Thus this commit
must be backported in every release where it is already present.
(cherry picked from commit 0274286dd3768c0d5e58588a1cb7e7e710fbc9d4)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit caaafd055edcbceb3d57ed9672b90900ec52a203)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/queue.c b/src/queue.c
index fb49676..1ef0607 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -336,14 +336,16 @@
}
/* Manages a server's connection queue. This function will try to dequeue as
- * many pending streams as possible, and wake them up.
+ * many pending streams as possible, and wake them up. <server_locked> must
+ * only be set if the caller already hold the server lock.
*/
-void process_srv_queue(struct server *s)
+void process_srv_queue(struct server *s, int server_locked)
{
struct proxy *p = s->proxy;
int maxconn;
- HA_SPIN_LOCK(SERVER_LOCK, &s->lock);
+ if (!server_locked)
+ HA_SPIN_LOCK(SERVER_LOCK, &s->lock);
HA_RWLOCK_WRLOCK(PROXY_LOCK, &p->lock);
maxconn = srv_dynamic_maxconn(s);
while (s->served < maxconn) {
@@ -352,7 +354,8 @@
break;
}
HA_RWLOCK_WRUNLOCK(PROXY_LOCK, &p->lock);
- HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
+ if (!server_locked)
+ HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
}
/* Adds the stream <strm> to the pending connection queue of server <strm>->srv