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netconsole: fix a deadlock with rtnl and netconsole's mutex

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This bug was introduced by commit
7a163bfb7c ("netconsole: avoid a crash with
multiple sysfs writers"). In store_enabled() we have the following
sequence: acquire nt->mutex then rtnl, but in the netconsole netdev
notifier we have rtnl then nt->mutex effectively leading to a deadlock.
The NULL pointer dereference that the above commit tries to fix is
actually due to another bug in netpoll_cleanup(). This is fixed by dropping
the mutex from the netdev notifier as it's already protected by rtnl.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Nikolay Aleksandrov 2013-09-19 15:02:36 +02:00 committed by David S. Miller
parent d0fe8c888b
commit c71380ff0b
1 changed files with 1 additions and 4 deletions
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5
drivers/net/netconsole.c
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@ -684,15 +684,12 @@ static int netconsole_netdev_event(struct notifier_block *this,
case NETDEV_RELEASE:
case NETDEV_JOIN:
case NETDEV_UNREGISTER:
/*
* rtnl_lock already held
/* rtnl_lock already held
* we might sleep in __netpoll_cleanup()
*/
spin_unlock_irqrestore(&target_list_lock, flags);
mutex_lock(&nt->mutex);
__netpoll_cleanup(&nt->np);
mutex_unlock(&nt->mutex);
spin_lock_irqsave(&target_list_lock, flags);
dev_put(nt->np.dev);