Luis reported this lockdep complaint, that he had also
reported earlier but when trying to analyse I had been
locking at the wrong code, and never saw the problem:
(slightly abridged)
=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.31-rc4-wl #6
-------------------------------------------------------
wpa_supplicant/3799 is trying to acquire lock:
(cfg80211_mutex){+.+.+.}, at: [<ffffffffa009246a>] cfg80211_get_dev_from_ifindex+0x1a/0x90 [cfg80211]
but task is already holding lock:
(rtnl_mutex){+.+.+.}, at: [<ffffffff81400ff2>] rtnl_lock+0x12/0x20
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (rtnl_mutex){+.+.+.}:
[<ffffffff810857b6>] __lock_acquire+0xd76/0x12b0
[<ffffffff81085dd3>] lock_acquire+0xe3/0x120
[<ffffffff814ee7a4>] mutex_lock_nested+0x44/0x350
[<ffffffff81400ff2>] rtnl_lock+0x12/0x20
[<ffffffffa009f6a5>] nl80211_send_reg_change_event+0x1f5/0x2a0 [cfg80211]
[<ffffffffa009529e>] set_regdom+0x28e/0x4c0 [cfg80211]
-> #0 (cfg80211_mutex){+.+.+.}:
[<ffffffff8108587b>] __lock_acquire+0xe3b/0x12b0
[<ffffffff81085dd3>] lock_acquire+0xe3/0x120
[<ffffffff814ee7a4>] mutex_lock_nested+0x44/0x350
[<ffffffffa009246a>] cfg80211_get_dev_from_ifindex+0x1a/0x90 [cfg80211]
[<ffffffffa009813f>] get_rdev_dev_by_info_ifindex+0x6f/0xa0 [cfg80211]
[<ffffffffa009b12b>] nl80211_set_interface+0x3b/0x260 [cfg80211]
When looking at the correct code, the problem is quite
obvious. I'm not entirely sure which code paths lead
here, so until I can analyse it better let's just use
RCU to avoid the problem.
Signed-off-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
---
net/wireless/nl80211.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- wireless-testing.orig/net/wireless/nl80211.c 2009-07-25 10:49:13.000000000 +0200
+++ wireless-testing/net/wireless/nl80211.c 2009-07-25 10:49:24.000000000 +0200
@@ -4517,10 +4517,10 @@ void nl80211_send_reg_change_event(struc
return;
}
- rtnl_lock();
+ rcu_read_lock();
genlmsg_multicast_allns(msg, 0, nl80211_regulatory_mcgrp.id,
- GFP_KERNEL);
- rtnl_unlock();
+ GFP_ATOMIC);
+ rcu_read_unlock();
return;
--
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