From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarek Poplawski Subject: [PATCH] pkt_sched: Fix qdisc_watchdog() vs. dev_deactivate() race Date: Wed, 20 Aug 2008 11:56:56 +0000 Message-ID: <20080820115656.GA7078@ff.dom.local> References: <20080819.040200.155911269.davem@davemloft.net> <20080819164830.GA2533@ami.dom.local> <20080819222329.GA10297@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , netdev@vger.kernel.org To: Herbert Xu Return-path: Received: from ik-out-1112.google.com ([66.249.90.181]:49767 "EHLO ik-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753321AbYHTL5D (ORCPT ); Wed, 20 Aug 2008 07:57:03 -0400 Received: by ik-out-1112.google.com with SMTP id c28so353038ika.5 for ; Wed, 20 Aug 2008 04:57:02 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20080819222329.GA10297@gondor.apana.org.au> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Aug 20, 2008 at 08:23:29AM +1000, Herbert Xu wrote: > On Tue, Aug 19, 2008 at 06:48:31PM +0200, Jarek Poplawski wrote: > > > > I can miss something, but probably it's needed in __netif_reschedule() > > No this is a genuine bug. However, it's also an old bug :) Even > with the locking and RCU barrier it could have occured. > > > yet. Here is a scenario: > > > > cpu1 cpu2 > > dev_deactivate() > > dev_deactivate_queue() > > qdisc_reset() > > qdisc_run() > > qdisc_watchdog_schedule() > > (or hrtimer_restart in cbq) > > We should add an aliveness check before scheduling the timer. This > is the slow path so adding a check shouldn't hurt. Thanks, Jarek P. ---------------> pkt_sched: Fix qdisc_watchdog() vs. dev_deactivate() race dev_deactivate() can skip rescheduling of a qdisc by qdisc_watchdog() or other timer calling netif_schedule() after dev_queue_deactivate(). We prevent this checking aliveness before scheduling the timer. With feedback from Herbert Xu Signed-off-by: Jarek Poplawski --- net/sched/sch_api.c | 3 +++ net/sched/sch_cbq.c | 3 +++ 2 files changed, 6 insertions(+), 0 deletions(-) diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index ef0efec..6f2bc7f 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -444,6 +444,9 @@ void qdisc_watchdog_schedule(struct qdisc_watchdog *wd, psched_time_t expires) { ktime_t time; + if (test_bit(__QDISC_STATE_DEACTIVATED, &qdisc_root(wd->qdisc)->state)) + return; + wd->qdisc->flags |= TCQ_F_THROTTLED; time = ktime_set(0, 0); time = ktime_add_ns(time, PSCHED_US2NS(expires)); diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c index 47ef492..c04d335 100644 --- a/net/sched/sch_cbq.c +++ b/net/sched/sch_cbq.c @@ -521,6 +521,9 @@ static void cbq_ovl_delay(struct cbq_class *cl) struct cbq_sched_data *q = qdisc_priv(cl->qdisc); psched_tdiff_t delay = cl->undertime - q->now; + if (test_bit(__QDISC_STATE_DEACTIVATED, &qdisc_root(cl->qdisc)->state)) + return; + if (!cl->delayed) { psched_time_t sched = q->now; ktime_t expires;