From: Patrick McHardy Date: Sun, 15 Jul 2007 03:49:26 +0000 (-0700) Subject: [NET_SCHED]: Revert "avoid transmit softirq on watchdog wakeup" optimization X-Git-Tag: v2.6.23-rc1~1054^2~10 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0621ed2e4edbe2f6f83dafbf85eecefae7aaf2e8;p=linux-2.6 [NET_SCHED]: Revert "avoid transmit softirq on watchdog wakeup" optimization As noticed by Ranko Zivojnovic , calling qdisc_run from the timer handler can result in deadlock: > CPU#0 > > qdisc_watchdog() fires and gets dev->queue_lock > qdisc_run()...qdisc_restart()... > -> releases dev->queue_lock and enters dev_hard_start_xmit() > > CPU#1 > > tc del qdisc dev ... > qdisc_graft()...dev_graft_qdisc()...dev_deactivate()... > -> grabs dev->queue_lock ... > > qdisc_reset()...{cbq,hfsc,htb,netem,tbf}_reset()...qdisc_watchdog_cancel()... > -> hrtimer_cancel() - waiting for the qdisc_watchdog() to exit, while still > holding dev->queue_lock > > CPU#0 > > dev_hard_start_xmit() returns ... > -> wants to get dev->queue_lock(!) > > DEADLOCK! The entire optimization is a bit questionable IMO, it moves potentially large parts of NET_TX_SOFTIRQ work to TIMER_SOFTIRQ/HRTIMER_SOFTIRQ, which kind of defeats the separation of them. Signed-off-by: Patrick McHardy Acked-by: Ranko Zivojnovic Signed-off-by: David S. Miller --- diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index d92ea26982..4fd0beca94 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -278,11 +278,7 @@ static enum hrtimer_restart qdisc_watchdog(struct hrtimer *timer) wd->qdisc->flags &= ~TCQ_F_THROTTLED; smp_wmb(); - if (spin_trylock(&dev->queue_lock)) { - qdisc_run(dev); - spin_unlock(&dev->queue_lock); - } else - netif_schedule(dev); + netif_schedule(dev); return HRTIMER_NORESTART; }