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pkt_sched: Prevent livelock in TX queue running.

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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>
This commit is contained in:
David S. Miller 2008-08-19 04:00:36 -07:00
parent d2805395aa
commit 195648bbc5
1 changed files with 3 additions and 1 deletions
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4
net/core/dev.c
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@ -1990,7 +1990,9 @@ static void net_tx_action(struct softirq_action *h)
qdisc_run(q);
spin_unlock(root_lock);
} else {
__netif_reschedule(q);
if (!test_bit(__QDISC_STATE_DEACTIVATED,
&q->state))
__netif_reschedule(q);
}
}
}