[PATCH net-next v2 02/13] wifi: cfg80211: use __rtnl_unlock in nl80211_pre_doit

[Stanislav Fomichev <sdf@fomichev.me>]

nl80211_pre_doit acquires rtnl_lock and then wiphy_lock, releasing
rtnl while keeping wiphy_lock held until post_doit. With the
introduction of rx_mode_wq and its flush in netdev_run_todo, calling
rtnl_unlock here creates a circular lock dependency:

  Chain exists of:
    (wq_completion)rx_mode_wq --> rtnl_mutex --> &rdev->wiphy.mtx

   Possible unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(&rdev->wiphy.mtx);
                                 lock(rtnl_mutex);
                                 lock(&rdev->wiphy.mtx);
    lock((wq_completion)rx_mode_wq);

Switch to __rtnl_unlock to skip netdev_run_todo in nl80211_pre_doit.
This seems safe because we run before the op.

Link: http://lore.kernel.org/netdev/69b5ad67.a00a0220.3b25d1.001a.GAE@google.com
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
---
 net/wireless/nl80211.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 2225f5d0b124..ce5f25d4c87e 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -18192,7 +18192,7 @@ static int nl80211_pre_doit(const struct genl_split_ops *ops,
 		__release(&rdev->wiphy.mtx);
 	}
 	if (!(internal_flags & NL80211_FLAG_NEED_RTNL))
-		rtnl_unlock();
+		__rtnl_unlock();
 
 	return 0;
 out_unlock:
-- 
2.53.0