Commit 195648bb authored Aug 19, 2008 by David S. Miller

pkt_sched: Prevent livelock in TX queue running.



If dev_deactivate() is trying to quiesce the queue, it
is theoretically possible for another cpu to livelock
trying to process that queue.  This happens because
dev_deactivate() grabs the queue spinlock as it checks
the queue state, whereas net_tx_action() does a trylock
and reschedules the qdisc if it hits the lock.

This breaks the livelock by adding a check on
__QDISC_STATE_DEACTIVATED to net_tx_action() when
the trylock fails.

Based upon feedback from Herbert Xu and Jarek Poplawski.

Signed-off-by: David S. Miller <davem@davemloft.net>

parent d2805395

net/core/dev.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -1990,6 +1990,8 @@ static void net_tx_action(struct softirq_action *h)
		qdisc_run(q);
		spin_unlock(root_lock);
		} else {
		if (!test_bit(__QDISC_STATE_DEACTIVATED,
		&q->state))
		__netif_reschedule(q);
		}
		}