Hi All, I am facing one issue with Linux kernel 4.0.4. *CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.0.4+ #19* This issue i am facing with below mentioned two scenario First Scenario: At the time when I start using PCIe based Atheros wifi card along with my Ethernet controller. If I am using both standalone then I am not facing this issue. (I think this is not hardware related issue as with the same combination of h/w but on different linux kernel version (3.4), I am not facing this issue.) Second Scenario: This issue also repeated if I keep on executing below mentioned command: # hostapd -B /etc/hostapd.conf My main focus is on first scenario. I googled it this issue and found that few people also faced this issue previously on Linux kernel 3.1/3.2/3.3 . Some people are saying that disabling IPv6 support from kernel configuration will resolve this issue but I need IPv6 support in my kernel due to project specific task. By digging out into Linux kernel and observing dump stack log(at the time CPU STALL), I found culprit function 'ieee80211_wake_queues_by_reason'. I go through the series of functions calling by this function, and stuck at one point. I found there are two 'rcu_read_lock();' in sequence. * So my question is can we call rcu_read_lock() function is sequence(two times) and later call rcu_read_unlock() one by one;??* Please look into the pictorial representation of my question: ieee80211_wake_queues_by_reason -- |----> __ieee80211_wake_queue ---> if (skb_queue_empty(&local->pending[queue])) { rcu_read_lock(); ieee80211_propagate_queue_wake(local, queue); rcu_read_unlock(); } ieee80211_propagate_queue_wake(local, queue) | --> netif_wake_subqueue(sdata->dev, ac) | --> rcu_read_lock(); q = rcu_dereference(txq->qdisc); __netif_schedule(q); rcu_read_unlock(); My Approach: I increased RCU stall time from 21 jiffies to 60 jiffies. -- CONFIG_RCU_CPU_STALL_TIMEOUT=21 ++ CONFIG_RCU_CPU_STALL_TIMEOUT=60 But this does not solve my problem. Please suggest me any approach to solve this problem. Thanks, Amit Gupta