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use separate barriers for "stop" and "listen" operations

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On some platforms, when a synchronizing barrier is cleared, one
thread can progress while other threads are still in the process
of releasing the barrier. If a barrier is reused by the progressing
thread during this window, it can cause a deadlock. This can occur if,
for example, we stop listening immediately after we start, because the
stop and listen functions both use socket->barrier.  This has been
addressed by using separate barrier objects for stop and listen.
This commit is contained in:
Evan Hunt
2023-01-07 16:30:21 -08:00
parent f0bba87db0
commit 9c577e10c3
4 changed files with 14 additions and 11 deletions
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5
lib/isc/netmgr/netmgr-int.h
View File

@@ -844,7 +844,8 @@ struct isc_nmsocket {
isc__networker_t *worker; isc__networker_t *worker;
isc_mutex_t lock; isc_mutex_t lock;
isc_barrier_t barrier; isc_barrier_t listen_barrier;
isc_barrier_t stop_barrier;
/*% Parent socket for multithreaded listeners */ /*% Parent socket for multithreaded listeners */
isc_nmsocket_t *parent; isc_nmsocket_t *parent;
@@ -1027,7 +1028,7 @@ struct isc_nmsocket {
atomic_int_fast32_t active_child_connections; atomic_int_fast32_t active_child_connections;
bool barrier_initialised; bool barriers_initialised;
bool manual_read_timer; bool manual_read_timer;
#ifdef NETMGR_TRACE #ifdef NETMGR_TRACE
void *backtrace[TRACE_SIZE]; void *backtrace[TRACE_SIZE];

12
lib/isc/netmgr/netmgr.c
View File

@@ -676,8 +676,9 @@ nmsocket_cleanup(isc_nmsocket_t *sock, bool dofree FLARG) {
#endif #endif
isc__nm_streamdns_cleanup_data(sock); isc__nm_streamdns_cleanup_data(sock);
if (sock->barrier_initialised) { if (sock->barriers_initialised) {
isc_barrier_destroy(&sock->barrier); isc_barrier_destroy(&sock->listen_barrier);
isc_barrier_destroy(&sock->stop_barrier);
} }
sock->magic = 0; sock->magic = 0;
@@ -2021,8 +2022,9 @@ isc__nmsocket_stop(isc_nmsocket_t *listener) {
void void
isc__nmsocket_barrier_init(isc_nmsocket_t *listener) { isc__nmsocket_barrier_init(isc_nmsocket_t *listener) {
REQUIRE(listener->nchildren > 0); REQUIRE(listener->nchildren > 0);
isc_barrier_init(&listener->barrier, listener->nchildren); isc_barrier_init(&listener->listen_barrier, listener->nchildren);
listener->barrier_initialised = true; isc_barrier_init(&listener->stop_barrier, listener->nchildren);
listener->barriers_initialised = true;
} }
void void
@@ -2032,7 +2034,7 @@ isc__nm_async_sockstop(isc__networker_t *worker, isc__netievent_t *ev0) {
UNUSED(worker); UNUSED(worker);
(void)atomic_fetch_sub(&listener->rchildren, 1); (void)atomic_fetch_sub(&listener->rchildren, 1);
isc_barrier_wait(&listener->barrier); isc_barrier_wait(&listener->stop_barrier);
} }
void void

4
lib/isc/netmgr/tcp.c
View File

@@ -556,7 +556,7 @@ done:
UNLOCK(&sock->parent->lock); UNLOCK(&sock->parent->lock);
REQUIRE(!worker->loop->paused); REQUIRE(!worker->loop->paused);
isc_barrier_wait(&sock->parent->barrier); isc_barrier_wait(&sock->parent->listen_barrier);
} }
static void static void
@@ -691,7 +691,7 @@ isc__nm_async_tcpstop(isc__networker_t *worker, isc__netievent_t *ev0) {
(void)atomic_fetch_sub(&sock->parent->rchildren, 1); (void)atomic_fetch_sub(&sock->parent->rchildren, 1);
REQUIRE(!worker->loop->paused); REQUIRE(!worker->loop->paused);
isc_barrier_wait(&sock->parent->barrier); isc_barrier_wait(&sock->parent->stop_barrier);
} }
void void

4
lib/isc/netmgr/udp.c
View File

@@ -427,7 +427,7 @@ done:
UNLOCK(&sock->parent->lock); UNLOCK(&sock->parent->lock);
REQUIRE(!worker->loop->paused); REQUIRE(!worker->loop->paused);
isc_barrier_wait(&sock->parent->barrier); isc_barrier_wait(&sock->parent->listen_barrier);
} }
static void static void
@@ -496,7 +496,7 @@ isc__nm_async_udpstop(isc__networker_t *worker, isc__netievent_t *ev0) {
(void)atomic_fetch_sub(&sock->parent->rchildren, 1); (void)atomic_fetch_sub(&sock->parent->rchildren, 1);
REQUIRE(!worker->loop->paused); REQUIRE(!worker->loop->paused);
isc_barrier_wait(&sock->parent->barrier); isc_barrier_wait(&sock->parent->stop_barrier);
} }
/* /*