When ath9k was switched over to use the mac80211 intermediate queues,
node cleanup now drains the mac80211 queues. However, this call path is
not protected by rcu_read_lock() as it was previously entirely internal
to the driver which uses its own locking.
This leads to a possible rcu_dereference() without holding
rcu_read_lock(); but only if a station is cleaned up while having
packets queued on the TXQ. Fix this by adding the rcu_read_lock() to the
caller in ath9k.
Fixes: 50f08edf9809 ("ath9k: Switch to using mac80211 intermediate software queues.") Cc: stable@vger.kernel.org Reported-by: Ben Greear <greearb@candelatech.com> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk> Signed-off-by: Kalle Valo <kvalo@codeaurora.org>