linux-kernel - Re: BUG: Bad page map in process udevd (anon

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Date:	Sat, 19 Feb 2011 18:01:36 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Michal Hocko <mhocko@...e.cz>, Ingo Molnar <mingo@...e.hu>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: BUG: Bad page map in process udevd (anon_vma: (null)) in 2.6.38-rc4

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Fri, Feb 18, 2011 at 10:22 PM, Eric W. Biederman
> <ebiederm@...ssion.com> wrote:
>>
>> It looks like the same problematic dellink pattern made it into net_namespace.c,
>> and your new LIST_DEBUG changes caught it.
>
> Hey, goodie. Committing that patch felt like locking the barn door
> after the horse had bolted, so I'm happy to hear it was actually worth
> it.
>
>> I will cook up a patch after I get some sleep.

After some sleep and some more looking I think I understand what is
going on and what is happening.

The first is that I was wrong about net_namespace.c being the culprit.
The list debug failures are new with Linus's patch and there is not a
single list_move net_namespace.c.

So this brings me back to unregister_netdevice_queue and the unreg_list.

In the beginning with batching unreg_list was a list that was used only
once in the lifetime of a network device (I think).  Now we have calls
using the unreg_list that can happen multiple times in the life of a
network device like dev_deactivate and dev_close that are also using the
unreg_list.  In addition in unregister_netdevice_queue we also do a
list_move because for devices like veth pairs it is possible that
unregister_netdevice_queue will be called multiple times.

So I think the change below to fix dev_deactivate which Eric D. missed
will fix this problem.  Now to go test that.

In other news my userspace is still very unhappy.  So it looks like I am
going to be tracking 2.6.38-rcN bugs for a while.

Eric

diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 8acba45..7a10a8d 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -1229,6 +1229,7 @@ void ieee80211_remove_interfaces(struct ieee80211_local *local)
 	}
 	mutex_unlock(&local->iflist_mtx);
 	unregister_netdevice_many(&unreg_list);
+	list_del(&unreg_list);
 }

 static u32 ieee80211_idle_off(struct ieee80211_local *local,
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 34dc598..1bc6980 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -839,6 +839,7 @@ void dev_deactivate(struct net_device *dev)

 	list_add(&dev->unreg_list, &single);
 	dev_deactivate_many(&single);
+	list_del(&single);
 }

 static void dev_init_scheduler_queue(struct net_device *dev,

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