From bc43b28c10855aa56f6d0bd64ec6a6d8edbcf11b Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Sat, 25 Jul 2009 10:54:13 +0200 Subject: [PATCH] cfg80211: fix circular lock dependency (1) 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: [] cfg80211_get_dev_from_ifindex+0x1a/0x90 [cfg80211] but task is already holding lock: (rtnl_mutex){+.+.+.}, at: [] rtnl_lock+0x12/0x20 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (rtnl_mutex){+.+.+.}: [] __lock_acquire+0xd76/0x12b0 [] lock_acquire+0xe3/0x120 [] mutex_lock_nested+0x44/0x350 [] rtnl_lock+0x12/0x20 [] nl80211_send_reg_change_event+0x1f5/0x2a0 [cfg80211] [] set_regdom+0x28e/0x4c0 [cfg80211] -> #0 (cfg80211_mutex){+.+.+.}: [] __lock_acquire+0xe3b/0x12b0 [] lock_acquire+0xe3/0x120 [] mutex_lock_nested+0x44/0x350 [] cfg80211_get_dev_from_ifindex+0x1a/0x90 [cfg80211] [] get_rdev_dev_by_info_ifindex+0x6f/0xa0 [cfg80211] [] 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 Signed-off-by: John W. Linville --- net/wireless/nl80211.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c index 7880a9c4cdda..283f1a890dad 100644 --- a/net/wireless/nl80211.c +++ b/net/wireless/nl80211.c @@ -4517,10 +4517,10 @@ void nl80211_send_reg_change_event(struct regulatory_request *request) 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; -- 2.20.1