From: Andrew Morton <[EMAIL PROTECTED]>
Date: Tue, 24 Apr 2007 12:42:50 -0700
> void debug_mutex_unlock(struct mutex *lock)
> {
> if (unlikely(!debug_locks))
> return;
>
> --> DEBUG_LOCKS_WARN_ON(lock->owner != current_thread_info());
> DEBUG_LOCKS_WARN_ON(lock->magic != lock);
>
> so it's complaining that cb_mutex is being release by a thread other than
> the one which acquired it. I'm unable to reproduce it with their config,
> naturally.
Is it illegal to sleep with a mutex held?
But I'm not so sure that is what is happening here.
net/core/rtnetlink.c does:
err = netlink_dump_start(rtnl, skb, nlh, dumpit, NULL);
here dumpit will be rtnl_dump_ifinfo.
Anyways, netlink_dump_start() will go:
mutex_lock(nlk->cb_mutex);
if (nlk->cb || sock_flag(sk, SOCK_DEAD)) {
mutex_unlock(nlk->cb_mutex);
netlink_destroy_callback(cb);
sock_put(sk);
return -EBUSY;
}
nlk->cb = cb;
mutex_unlock(nlk->cb_mutex);
Nothing there sleeps. Then it does netlink_dump():
mutex_lock(nlk->cb_mutex);
cb = nlk->cb;
if (cb == NULL) {
err = -EINVAL;
goto errout_skb;
}
len = cb->dump(skb, cb);
if (len > 0) {
mutex_unlock(nlk->cb_mutex);
skb_queue_tail(&sk->sk_receive_queue, skb);
sk->sk_data_ready(sk, len);
return 0;
}
nlh = nlmsg_put_answer(skb, cb, NLMSG_DONE, sizeof(len), NLM_F_MULTI);
if (!nlh)
goto errout_skb;
memcpy(nlmsg_data(nlh), &len, sizeof(len));
skb_queue_tail(&sk->sk_receive_queue, skb);
sk->sk_data_ready(sk, skb->len);
if (cb->done)
cb->done(cb);
nlk->cb = NULL;
mutex_unlock(nlk->cb_mutex);
This invokes rtnl_dump_ifinfo() via cb->dump() which just fills
data into the packet.
There are some wakeups and other bits there, but nothing that
should mess with the nlk->cb_mutex or sleep.
I think I see what might be the problem, nlk->cb_mutex is set
to "rtnl_mutex" and this is used for other purposes in various
code paths here, maybe there is a double mutex_unlock() or
similar due to that?
Patrick?
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