[ 24/48] cfg80211: fix potential deadlock in regulatory

Ben Hutchings
2012-07-01T18:18:55Z

From: Eliad Peller <eliad@wizery.com>

commit fe20b39ec32e975f1054c0b7866c873a954adf05 upstream.

reg_timeout_work() calls restore_regulatory_settings() which
takes cfg80211_mutex.

reg_set_request_processed() already holds cfg80211_mutex
before calling cancel_delayed_work_sync(reg_timeout),
so it might deadlock.

Call the async cancel_delayed_work instead, in order
to avoid the potential deadlock.

This is the relevant lockdep warning:

cfg80211: Calling CRDA for country: XX

======================================================
[ INFO: possible circular locking dependency detected ]
3.4.0-rc5-wl+ #26 Not tainted
-------------------------------------------------------
kworker/0:2/1391 is trying to acquire lock:
(cfg80211_mutex){+.+.+.}, at: [<bf28ae00>] restore_regulatory_settings+0x34/0x418 [cfg80211]

but task is already holding lock:
((reg_timeout).work){+.+...}, at: [<c0059e94>] process_one_work+0x1f0/0x480

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 ((reg_timeout).work){+.+...}:
[<c008fd44>] validate_chain+0xb94/0x10f0
[<c0090b68>] __lock_acquire+0x8c8/0x9b0
[<c0090d40>] lock_acquire+0xf0/0x114
[<c005b600>] wait_on_work+0x4c/0x154
[<c005c000>] __cancel_work_timer+0xd4/0x11c
[<c005c064>] cancel_delayed_work_sync+0x1c/0x20
[<bf28b274>] reg_set_request_processed+0x50/0x78 [cfg80211]
[<bf28bd84>] set_regdom+0x550/0x600 [cfg80211]
[<bf294cd8>] nl80211_set_reg+0x218/0x258 [cfg80211]
[<c03c7738>] genl_rcv_msg+0x1a8/0x1e8
[<c03c6a00>] netlink_rcv_skb+0x5c/0xc0
[<c03c7584>] genl_rcv+0x28/0x34
[<c03c6720>] netlink_unicast+0x15c/0x228
[<c03c6c7c>] netlink_sendmsg+0x218/0x298
[<c03933c8>] sock_sendmsg+0xa4/0xc0
[<c039406c>] __sys_sendmsg+0x1e4/0x268
[<c0394228>] sys_sendmsg+0x4c/0x70
[<c0013840>] ret_fast_syscall+0x0/0x3c

-> #1 (reg_mutex){+.+.+.}:
[<c008fd44>] validate_chain+0xb94/0x10f0
[<c0090b68>] __lock_acquire+0x8c8/0x9b0
[<c0090d40>] lock_acquire+0xf0/0x114
[<c04734dc>] mutex_lock_nested+0x48/0x320
[<bf28b2cc>] reg_todo+0x30/0x538 [cfg80211]
[<c0059f44>] process_one_work+0x2a0/0x480
[<c005a4b4>] worker_thread+0x1bc/0x2bc
[<c0061148>] kthread+0x98/0xa4
[<c0014af4>] kernel_thread_exit+0x0/0x8

-> #0 (cfg80211_mutex){+.+.+.}:
[<c008ed58>] print_circular_bug+0x68/0x2cc
[<c008fb28>] validate_chain+0x978/0x10f0
[<c0090b68>] __lock_acquire+0x8c8/0x9b0
[<c0090d40>] lock_acquire+0xf0/0x114
[<c04734dc>] mutex_lock_nested+0x48/0x320
[<bf28ae00>] restore_regulatory_settings+0x34/0x418 [cfg80211]
[<bf28b200>] reg_timeout_work+0x1c/0x20 [cfg80211]
[<c0059f44>] process_one_work+0x2a0/0x480
[<c005a4b4>] worker_thread+0x1bc/0x2bc
[<c0061148>] kthread+0x98/0xa4
[<c0014af4>] kernel_thread_exit+0x0/0x8

other info that might help us debug this:

Chain exists of:
cfg80211_mutex --> reg_mutex --> (reg_timeout).work

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock((reg_timeout).work);
lock(reg_mutex);
lock((reg_timeout).work);
lock(cfg80211_mutex);

*** DEADLOCK ***

2 locks held by kworker/0:2/1391:
#0: (events){.+.+.+}, at: [<c0059e94>] process_one_work+0x1f0/0x480
#1: ((reg_timeout).work){+.+...}, at: [<c0059e94>] process_one_work+0x1f0/0x480

stack backtrace:
[<c001b928>] (unwind_backtrace+0x0/0x12c) from [<c0471d3c>] (dump_stack+0x20/0x24)
[<c0471d3c>] (dump_stack+0x20/0x24) from [<c008ef70>] (print_circular_bug+0x280/0x2cc)
[<c008ef70>] (print_circular_bug+0x280/0x2cc) from [<c008fb28>] (validate_chain+0x978/0x10f0)
[<c008fb28>] (validate_chain+0x978/0x10f0) from [<c0090b68>] (__lock_acquire+0x8c8/0x9b0)
[<c0090b68>] (__lock_acquire+0x8c8/0x9b0) from [<c0090d40>] (lock_acquire+0xf0/0x114)
[<c0090d40>] (lock_acquire+0xf0/0x114) from [<c04734dc>] (mutex_lock_nested+0x48/0x320)
[<c04734dc>] (mutex_lock_nested+0x48/0x320) from [<bf28ae00>] (restore_regulatory_settings+0x34/0x418 [cfg80211])
[<bf28ae00>] (restore_regulatory_settings+0x34/0x418 [cfg80211]) from [<bf28b200>] (reg_timeout_work+0x1c/0x20 [cfg80211])
[<bf28b200>] (reg_timeout_work+0x1c/0x20 [cfg80211]) from [<c0059f44>] (process_one_work+0x2a0/0x480)
[<c0059f44>] (process_one_work+0x2a0/0x480) from [<c005a4b4>] (worker_thread+0x1bc/0x2bc)
[<c005a4b4>] (worker_thread+0x1bc/0x2bc) from [<c0061148>] (kthread+0x98/0xa4)
[<c0061148>] (kthread+0x98/0xa4) from [<c0014af4>] (kernel_thread_exit+0x0/0x8)
cfg80211: Calling CRDA to update world regulatory domain
cfg80211: World regulatory domain updated:
cfg80211: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp)
cfg80211: (2402000 KHz - 2472000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
cfg80211: (2457000 KHz - 2482000 KHz @ 20000 KHz), (300 mBi, 2000 mBm)
cfg80211: (2474000 KHz - 2494000 KHz @ 20000 KHz), (300 mBi, 2000 mBm)
cfg80211: (5170000 KHz - 5250000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
cfg80211: (5735000 KHz - 5835000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/wireless/reg.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/wireless/reg.c b/net/wireless/reg.c
index 15f3474..baf5704 100644
--- a/net/wireless/reg.c
+++ b/net/wireless/reg.c
@@ -1389,7 +1389,7 @@ static void reg_set_request_processed(void)
spin_unlock(&reg_requests_lock);

if (last_request->initiator == NL80211_REGDOM_SET_BY_USER)
- cancel_delayed_work_sync(&reg_timeout);
+ cancel_delayed_work(&reg_timeout);

if (need_more_processing)
schedule_work(&reg_work);