mac80211: avoid deadlock revealed by lockdep

mac80211: avoid deadlock revealed by lockdep

sdata->u.ap.request_smps_work can’t be flushed synchronously
under wdev_lock(wdev) since ieee80211_request_smps_ap_work
itself locks the same lock.
While at it, reset the driver_smps_mode when the ap is
stopped to its default: OFF.

This solves:

======================================================
[ INFO: possible circular locking dependency detected ]
3.12.0-ipeer+ #2 Tainted: G           O
-------------------------------------------------------
rmmod/2867 is trying to acquire lock:
  ((&sdata->u.ap.request_smps_work)){+.+...}, at: [<c105b8d0>] flush_work+0x0/0x90

but task is already holding lock:
  (&wdev->mtx){+.+.+.}, at: [<f9b32626>] cfg80211_stop_ap+0x26/0x230 [cfg80211]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&wdev->mtx){+.+.+.}:
        [<c10aefa9>] lock_acquire+0x79/0xe0
        [<c1607a1a>] mutex_lock_nested+0x4a/0x360
        [<fb06288b>] ieee80211_request_smps_ap_work+0x2b/0x50 [mac80211]
        [<c105cdd8>] process_one_work+0x198/0x450
        [<c105d469>] worker_thread+0xf9/0x320
        [<c10669ff>] kthread+0x9f/0xb0
        [<c1613397>] ret_from_kernel_thread+0x1b/0x28

-> #0 ((&sdata->u.ap.request_smps_work)){+.+...}:
        [<c10ae9df>] __lock_acquire+0x183f/0x1910
        [<c10aefa9>] lock_acquire+0x79/0xe0
        [<c105b917>] flush_work+0x47/0x90
        [<c105d867>] __cancel_work_timer+0x67/0xe0
        [<c105d90f>] cancel_work_sync+0xf/0x20
        [<fb0765cc>] ieee80211_stop_ap+0x8c/0x340 [mac80211]
        [<f9b3268c>] cfg80211_stop_ap+0x8c/0x230 [cfg80211]
        [<f9b0d8f9>] cfg80211_leave+0x79/0x100 [cfg80211]
        [<f9b0da72>] cfg80211_netdev_notifier_call+0xf2/0x4f0 [cfg80211]
        [<c160f2c9>] notifier_call_chain+0x59/0x130
        [<c106c6de>] __raw_notifier_call_chain+0x1e/0x30
        [<c106c70f>] raw_notifier_call_chain+0x1f/0x30
        [<c14f8213>] call_netdevice_notifiers_info+0x33/0x70
        [<c14f8263>] call_netdevice_notifiers+0x13/0x20
        [<c14f82a4>] __dev_close_many+0x34/0xb0
        [<c14f83fe>] dev_close_many+0x6e/0xc0
        [<c14f9c77>] rollback_registered_many+0xa7/0x1f0
        [<c14f9dd4>] unregister_netdevice_many+0x14/0x60
        [<fb06f4d9>] ieee80211_remove_interfaces+0xe9/0x170 [mac80211]
        [<fb055116>] ieee80211_unregister_hw+0x56/0x110 [mac80211]
        [<fa3e9396>] iwl_op_mode_mvm_stop+0x26/0xe0 [iwlmvm]
        [<f9b9d8ca>] _iwl_op_mode_stop+0x3a/0x70 [iwlwifi]
        [<f9b9d96f>] iwl_opmode_deregister+0x6f/0x90 [iwlwifi]
        [<fa405179>] __exit_compat+0xd/0x19 [iwlmvm]
        [<c10b8bf9>] SyS_delete_module+0x179/0x2b0
        [<c1613421>] sysenter_do_call+0x12/0x32

Fixes: 687da132234f ("mac80211: implement SMPS for AP")
Cc: <stable@vger.kernel.org> [3.13]
Reported-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>