Jiri Kosina wrote:
On Mon, 18 Feb 2008, Laszlo Attila Toth wrote:
Okay, but I can't figure out what's the problem with it. I don't have
wireless card on my linux box also I can't test it but everything else
works. Swap is mounted. The concurrency cannot be a problem because the
write operation is protected by a lock.
- write_lock_bh(&dev_base_lock);
- dev->link_mode = nla_get_u8(tb[IFLA_LINKMODE]);
- write_unlock_bh(&dev_base_lock);
+ if (dev->link_mode != nla_get_u8(tb[IFLA_LINKMODE])) {
+ write_lock_bh(&dev_base_lock);
+ dev->link_mode = nla_get_u8(tb[IFLA_LINKMODE]);
+ write_lock_bh(&dev_base_lock);
+ modified = 1;
+ }
}
1) you are accessing dev->link_mode and tb[] outside the dev_base_lock
yes, because tb[IFLA_LINKMODE] is not used by someone else in this case
only dev->link_mode. Although its value is unpredictable in case of a
concurrent access in the condition, it does not affect the final value
of dev->link_mode but the length of the critical section remains
minimal. The if statement may be inside the lock.
2) there is obvious and immediate deadlock -- you acquire the
dev_base_lock twice, without any unlock, just look at the chunk above
Indeed:
"Feb 16 16:51:49 sandman kernel: BUG: rwlock recursion on CPU#0,"
I missed it. I copied the code from another patch which didn't contain
the two locking statements and when I copied them back it became a
copy-paste bug.
3) even with this deadlock fixed, Rafael states that either NM or
wpa_supplicant (I don't recall from top of my head) still don't work
That's bad. Does my suggestion solve the problem? Again:
- if (modified)
- netdev_state_change(dev);
+ if (modified && dev->flags & IFF_UP)
+ call_netdevice_notifiers(NETDEV_CHANGE, dev)
Regards,
Attila
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