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Fix races with backend_retry

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This commit is contained in:
Ondřej Kuzník 2018-07-24 09:56:52 +01:00
parent c087244265
commit 81ead4a5f4
1 changed files with 41 additions and 11 deletions
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52
servers/lloadd/backend.c
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@ -38,6 +38,12 @@ upstream_connect_cb( evutil_socket_t s, short what, void *arg )
Debug( LDAP_DEBUG_CONNS, "upstream_connect_cb: "
"fd=%d connection callback for backend uri='%s'\n",
s, b->b_uri.bv_val );
if ( s != conn->fd ) {
/* backend_reset has been here first */
goto preempted;
}
if ( what == EV_WRITE ) {
socklen_t optlen = sizeof(error);
@ -74,9 +80,8 @@ done:
error ? sock_errstr( error, ebuf, sizeof(ebuf) ) : "" );
}
backend_retry( b );
} else {
b->b_failed = 0;
}
preempted:
ldap_pvt_thread_mutex_unlock( &b->b_mutex );
event_free( conn->event );
@ -485,22 +490,39 @@ backend_connect_task( void *ctx, void *arg )
}
/*
* Needs exclusive access to the backend.
* Needs exclusive access to the backend and no other thread is allowed to call
* backend_retry while we're handling this.
*
* If gentle == 0, a full pause must be in effect, else we risk deadlocking on
* event_free().
*/
void
backend_reset( LloadBackend *b, int gentle )
{
if ( b->b_cookie ) {
int rc;
rc = ldap_pvt_thread_pool_retract( b->b_cookie );
assert( rc == 1 );
b->b_cookie = NULL;
b->b_opening--;
if ( ldap_pvt_thread_pool_retract( b->b_cookie ) ) {
b->b_cookie = NULL;
b->b_opening--;
} else {
/*
* The task might not be cancelable because it just started
* executing.
*
* Shutdown should be the only time when the thread pool is
* in that state. Keep the cookie in to keep an eye on whether
* it's finished yet.
*/
assert( slapd_shutdown );
}
}
/* Not safe to hold our mutex and call event_del/free if the event's
* callback is running, relinquish the mutex while we do so. */
if ( b->b_retry_event &&
event_pending( b->b_retry_event, EV_TIMEOUT, NULL ) ) {
assert( b->b_failed );
ldap_pvt_thread_mutex_unlock( &b->b_mutex );
event_del( b->b_retry_event );
ldap_pvt_thread_mutex_lock( &b->b_mutex );
b->b_opening--;
}
if ( b->b_dns_req ) {
@ -515,16 +537,24 @@ backend_reset( LloadBackend *b, int gentle )
"destroying socket pending connect() fd=%d\n",
pending->fd );
event_free( pending->event );
event_active( pending->event, EV_WRITE, 0 );
evutil_closesocket( pending->fd );
pending->fd = -1;
LDAP_LIST_REMOVE( pending, next );
ch_free( pending );
if ( !gentle ) {
/* None of the event bases are running, we're safe to free the
* event right now and potentially free the backend itself */
event_free( pending->event );
ch_free( pending );
}
/* else, just let the event dispose of the resources on its own later */
b->b_opening--;
}
connections_walk(
&b->b_mutex, &b->b_preparing, lload_connection_close, &gentle );
assert( LDAP_CIRCLEQ_EMPTY( &b->b_preparing ) );
assert( b->b_opening == 0 );
assert( b->b_opening == ( b->b_cookie ? 1 : 0 ) );
b->b_failed = 0;
connections_walk_last( &b->b_mutex, &b->b_bindconns, b->b_last_bindconn,