From: Patrick McHardy <[email protected]>
[NET_SCHED]: Revert "avoid transmit softirq on watchdog wakeup" optimization
As noticed by Ranko Zivojnovic <[email protected]>, 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 <[email protected]>
Acked-by: Ranko Zivojnovic <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
net/sched/sch_api.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -290,11 +290,7 @@ static enum hrtimer_restart qdisc_watchd
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;
}
--
-
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