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authorHerbert Xu <herbert@gondor.apana.org.au>2006-09-18 00:22:30 -0700
committerDavid S. Miller <davem@davemloft.net>2006-09-18 00:22:30 -0700
commitd7811e623dd4be3e3bdba2d6330f7f15541ee45f (patch)
treef43bafe2e8d7e43b2cc3f4cb7dcda4c5e8815630
parentcbe21d8fefca605b90e34f0f019505e599712f9b (diff)
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[NET]: Drop tx lock in dev_watchdog_up
Fix lockdep warning with GRE, iptables and Speedtouch ADSL, PPP over ATM. On Sat, Sep 02, 2006 at 08:39:28PM +0000, Krzysztof Halasa wrote: > > ======================================================= > [ INFO: possible circular locking dependency detected ] > ------------------------------------------------------- > swapper/0 is trying to acquire lock: > (&dev->queue_lock){-+..}, at: [<c02c8c46>] dev_queue_xmit+0x56/0x290 > > but task is already holding lock: > (&dev->_xmit_lock){-+..}, at: [<c02c8e14>] dev_queue_xmit+0x224/0x290 > > which lock already depends on the new lock. This turns out to be a genuine bug. The queue lock and xmit lock are intentionally taken out of order. Two things are supposed to prevent dead-locks from occuring: 1) When we hold the queue_lock we're supposed to only do try_lock on the tx_lock. 2) We always drop the queue_lock after taking the tx_lock and before doing anything else. > > the existing dependency chain (in reverse order) is: > > -> #1 (&dev->_xmit_lock){-+..}: > [<c012e7b6>] lock_acquire+0x76/0xa0 > [<c0336241>] _spin_lock_bh+0x31/0x40 > [<c02d25a9>] dev_activate+0x69/0x120 This path obviously breaks assumption 1) and therefore can lead to ABBA dead-locks. I've looked at the history and there seems to be no reason for the lock to be held at all in dev_watchdog_up. The lock appeared in day one and even there it was unnecessary. In fact, people added __dev_watchdog_up precisely in order to get around the tx lock there. The function dev_watchdog_up is already serialised by rtnl_lock since its only caller dev_activate is always called under it. So here is a simple patch to remove the tx lock from dev_watchdog_up. In 2.6.19 we can eliminate the unnecessary __dev_watchdog_up and replace it with dev_watchdog_up. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/sched/sch_generic.c2
1 files changed, 0 insertions, 2 deletions
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 0834c2ee9174..6f9151899795 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -238,9 +238,7 @@ void __netdev_watchdog_up(struct net_device *dev)
static void dev_watchdog_up(struct net_device *dev)
{
- netif_tx_lock_bh(dev);
__netdev_watchdog_up(dev);
- netif_tx_unlock_bh(dev);
}
static void dev_watchdog_down(struct net_device *dev)