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wifi: ath11k: fix RCU documentation in ath11k_mac_op_ipv6_changed()

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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: feafe59c89 ("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>
Link: https://msgid.link/20240531022411.6543-1-quic_bqiang@quicinc.com
This commit is contained in:
Baochen Qiang
2024-06-11 09:42:33 +03:00
committed by Kalle Valo
parent 8b2a12749b
commit 53d7c99719
1 changed files with 6 additions and 1 deletions
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7
drivers/net/wireless/ath/ath11k/mac.c
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@@ -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));