| Message ID | 20240531022411.6543-1-quic_bqiang@quicinc.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 53d7c99719e29819eaeb9f373d262a6b56ea7cce |
| Delegated to: | Kalle Valo |
| Headers | show |
| Series | wifi: ath11k: fix RCU documentation in ath11k_mac_op_ipv6_changed() | expand |
On 5/30/2024 7:24 PM, Baochen Qiang wrote: > 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 <quic_bqiang@quicinc.com> Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Baochen Qiang <quic_bqiang@quicinc.com> wrote: > 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 <quic_bqiang@quicinc.com> > Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com> > Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com> Patch applied to ath-next branch of ath.git, thanks. 53d7c99719e2 wifi: ath11k: fix RCU documentation in ath11k_mac_op_ipv6_changed()
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));
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 <quic_bqiang@quicinc.com> --- drivers/net/wireless/ath/ath11k/mac.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) base-commit: 6e7a5c6d5e38b93f9cc3289d66a597b9a4ca0403