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BUG/MEDIUM: threads/unix: Fix a deadlock when a listener is temporarily disabled

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When a listener is temporarily disabled, we start by locking it and then we call
.pause callback of the underlying protocol (tcp/unix). For TCP listeners, this
is not a problem. But listeners bound on an unix socket are in fact closed
instead. So .pause callback relies on unbind_listener function to do its job.

Unfortunatly, unbind_listener hold the listener's lock and then call an internal
function to unbind it. So, there is a deadlock here. This happens during a
reload. To fix the problemn, the function do_unbind_listener, which is lockless,
is now exported and is called when a listener bound on an unix socket is
temporarily disabled.

This patch must be backported in 1.8.
This commit is contained in:
Christopher Faulet 2018-03-16 10:04:47 +01:00 committed by Willy Tarreau
parent 4288c5a9d8
commit 510c0d67ef
3 changed files with 18 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/proto/listener.h
View File

@ -60,6 +60,11 @@ int disable_all_listeners(struct protocol *proto);
/* Dequeues all of the listeners waiting for a resource in wait queue <queue>. */
void dequeue_all_listeners(struct list *list);
/* Must be called with the lock held. Depending on <do_close> value, it does
* what unbind_listener or unbind_listener_no_close should do.
*/
void do_unbind_listener(struct listener *listener, int do_close);
/* This function closes the listening socket for the specified listener,
* provided that it's already in a listening state. The listener enters the
* LI_ASSIGNED state. This function is intended to be used as a generic

23
src/listener.c
View File

@ -49,8 +49,6 @@ static struct bind_kw_list bind_keywords = {
struct xfer_sock_list *xfer_sock_list = NULL;
static void __do_unbind_listener(struct listener *listener, int do_close);
/* This function adds the specified listener's file descriptor to the polling
* lists if it is in the LI_LISTEN state. The listener enters LI_READY or
* LI_FULL state depending on its number of connections. In deamon mode, we
@ -68,9 +66,9 @@ static void enable_listener(struct listener *listener)
* want any fd event to reach it.
*/
if (!(global.tune.options & GTUNE_SOCKET_TRANSFER))
__do_unbind_listener(listener, 1);
do_unbind_listener(listener, 1);
else {
__do_unbind_listener(listener, 0);
do_unbind_listener(listener, 0);
listener->state = LI_LISTEN;
}
}
@ -308,8 +306,10 @@ void dequeue_all_listeners(struct list *list)
HA_SPIN_UNLOCK(LISTENER_QUEUE_LOCK, &lq_lock);
}
/* must be called with the lock held */
static void __do_unbind_listener(struct listener *listener, int do_close)
/* Must be called with the lock held. Depending on <do_close> value, it does
* what unbind_listener or unbind_listener_no_close should do.
*/
void do_unbind_listener(struct listener *listener, int do_close)
{
if (listener->state == LI_READY)
fd_stop_recv(listener->fd);
@ -331,13 +331,6 @@ static void __do_unbind_listener(struct listener *listener, int do_close)
}
}
static void do_unbind_listener(struct listener *listener, int do_close)
{
HA_SPIN_LOCK(LISTENER_LOCK, &listener->lock);
__do_unbind_listener(listener, do_close);
HA_SPIN_UNLOCK(LISTENER_LOCK, &listener->lock);
}
/* This function closes the listening socket for the specified listener,
* provided that it's already in a listening state. The listener enters the
* LI_ASSIGNED state. This function is intended to be used as a generic
@ -345,7 +338,9 @@ static void do_unbind_listener(struct listener *listener, int do_close)
*/
void unbind_listener(struct listener *listener)
{
HA_SPIN_LOCK(LISTENER_LOCK, &listener->lock);
do_unbind_listener(listener, 1);
HA_SPIN_UNLOCK(LISTENER_LOCK, &listener->lock);
}
/* This function pretends the listener is dead, but keeps the FD opened, so
@ -353,7 +348,9 @@ void unbind_listener(struct listener *listener)
*/
void unbind_listener_no_close(struct listener *listener)
{
HA_SPIN_LOCK(LISTENER_LOCK, &listener->lock);
do_unbind_listener(listener, 0);
HA_SPIN_UNLOCK(LISTENER_LOCK, &listener->lock);
}
/* This function closes all listening sockets bound to the protocol <proto>,

4
src/proto_uxst.c
View File

@ -393,7 +393,9 @@ static int uxst_pause_listener(struct listener *l)
if (((struct sockaddr_un *)&l->addr)->sun_path[0])
return 1;
unbind_listener(l);
/* Listener's lock already held. Call lockless version of
* unbind_listener. */
do_unbind_listener(l, 1);
return 0;
}