From 53d7c99719e29819eaeb9f373d262a6b56ea7cce Mon Sep 17 00:00:00 2001 From: Baochen Qiang Date: Tue, 11 Jun 2024 09:42:33 +0300 Subject: wifi: ath11k: fix RCU documentation in ath11k_mac_op_ipv6_changed() Current documentation on RCU in ath11k_mac_op_ipv6_changed() says: /* Note: read_lock_bh() calls rcu_read_lock() */ read_lock_bh(&idev->lock); This is wrong because without enabling CONFIG_PREEMPT_RT rcu_read_lock() is not called by read_lock_bh(). The reason why current code works even in a CONFIG_PREEMPT_RT=n kernel is because atomic_notifier_call_chain() already does that for us, see: int atomic_notifier_call_chain() { ... rcu_read_lock(); ret = notifier_call_chain(&nh->head, val, v, -1, NULL); rcu_read_unlock(); ... } and backtrace: ath11k_mac_op_ipv6_changed ieee80211_ifa6_changed notifier_call_chain atomic_notifier_call_chain So update the comment to make it correct. This is found during code review, compile tested only. Fixes: feafe59c8975 ("wifi: ath11k: use RCU when accessing struct inet6_dev::ac_list") Signed-off-by: Baochen Qiang Acked-by: Jeff Johnson Signed-off-by: Kalle Valo Link: https://msgid.link/20240531022411.6543-1-quic_bqiang@quicinc.com --- drivers/net/wireless/ath/ath11k/mac.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/net/wireless/ath/ath11k/mac.c b/drivers/net/wireless/ath/ath11k/mac.c index a1800c75d32b..29af015a16f9 100644 --- a/drivers/net/wireless/ath/ath11k/mac.c +++ b/drivers/net/wireless/ath/ath11k/mac.c @@ -9020,7 +9020,12 @@ static void ath11k_mac_op_ipv6_changed(struct ieee80211_hw *hw, offload = &arvif->arp_ns_offload; count = 0; - /* Note: read_lock_bh() calls rcu_read_lock() */ + /* The _ipv6_changed() is called with RCU lock already held in + * atomic_notifier_call_chain(), so we don't need to call + * rcu_read_lock() again here. But note that with CONFIG_PREEMPT_RT + * enabled, read_lock_bh() also calls rcu_read_lock(). This is OK + * because RCU read critical section is allowed to get nested. + */ read_lock_bh(&idev->lock); memset(offload->ipv6_addr, 0, sizeof(offload->ipv6_addr)); -- cgit v1.2.3-58-ga151