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>
diff --git a/net/core/dev.c b/net/core/dev.c
index 8d13380..60c51f7 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1990,7 +1990,9 @@
qdisc_run(q);
spin_unlock(root_lock);
} else {
- __netif_reschedule(q);
+ if (!test_bit(__QDISC_STATE_DEACTIVATED,
+ &q->state))
+ __netif_reschedule(q);
}
}
}