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Revert "MEDIUM: queue: make pendconn_process_next_strm() only return the pendconn"

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This reverts commit 5304669e1b.

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.
This commit is contained in:
Willy Tarreau 2021-06-24 07:27:01 +02:00
parent d83c98eb14
commit a48905bad8
1 changed files with 17 additions and 25 deletions
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42
src/queue.c
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@ -254,14 +254,11 @@ static struct pendconn *pendconn_first(struct eb_root *pendconns)
* to <srv>.
*
* This function must only be called if the server queue _AND_ the proxy queue
* are locked. 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
* server's list, to update the LB algo, update ->served, and to wake up the
* stream's task.
* are locked. Today it is only called by process_srv_queue. When a pending
* connection is dequeued, this function returns 1 if the pending connection can
* be handled by the current thread, else it returns 2.
*/
static struct pendconn *pendconn_process_next_strm(struct server *srv, struct proxy *px)
static int pendconn_process_next_strm(struct server *srv, struct proxy *px)
{
struct pendconn *p = NULL;
struct pendconn *pp = NULL;
@ -284,7 +281,7 @@ static struct pendconn *pendconn_process_next_strm(struct server *srv, struct pr
pp = pendconn_first(&px->queue.head);
if (!p && !pp)
return NULL;
return 0;
else if (!pp)
goto use_p; /* p != NULL */
else if (!p)
@ -326,8 +323,17 @@ static struct pendconn *pendconn_process_next_strm(struct server *srv, struct pr
unlinked:
p->strm_flags |= SF_ASSIGNED;
p->target = srv;
_HA_ATOMIC_INC(&srv->served);
_HA_ATOMIC_INC(&srv->proxy->served);
__ha_barrier_atomic_store();
return p;
if (px->lbprm.server_take_conn)
px->lbprm.server_take_conn(srv);
stream_add_srv_conn(p->strm, srv);
task_wakeup(p->strm->task, TASK_WOKEN_RES);
return 1;
}
/* Manages a server's connection queue. This function will try to dequeue as
@ -337,7 +343,6 @@ static struct pendconn *pendconn_process_next_strm(struct server *srv, struct pr
void process_srv_queue(struct server *s, int server_locked)
{
struct proxy *p = s->proxy;
int done = 0;
int maxconn;
if (!server_locked)
@ -345,26 +350,13 @@ void process_srv_queue(struct server *s, int server_locked)
HA_RWLOCK_WRLOCK(PROXY_LOCK, &p->lock);
maxconn = srv_dynamic_maxconn(s);
while (s->served < maxconn) {
struct pendconn *pc;
pc = pendconn_process_next_strm(s, p);
if (!pc)
int ret = pendconn_process_next_strm(s, p);
if (!ret)
break;
done = 1;
_HA_ATOMIC_INC(&s->served);
_HA_ATOMIC_INC(&p->served);
stream_add_srv_conn(pc->strm, s);
task_wakeup(pc->strm->task, TASK_WOKEN_RES);
}
HA_RWLOCK_WRUNLOCK(PROXY_LOCK, &p->lock);
if (!server_locked)
HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
if (done && p->lbprm.server_take_conn)
p->lbprm.server_take_conn(s);
}
/* Adds the stream <strm> to the pending connection queue of server <strm>->srv