Re: [PATCH] wifi: ath12k: fix false positive RCU warning on PREEMPT_RT

[Baochen Qiang <baochen.qiang@oss.qualcomm.com>]

On 4/21/2026 12:10 AM, Yu-Hsiang Tseng wrote:
> ath12k_mac_get_arvif() asserts that the caller holds an RCU read lock:
> 
>     WARN_ON(!rcu_read_lock_any_held());
> 
> On PREEMPT_RT kernels built with CONFIG_PROVE_RCU=n, this produces a
> false positive splat whenever firmware stats events are processed,
> even though the caller does hold the RCU read lock.
> 
> Root cause:
> 
>   - On !PROVE_RCU, rcu_read_lock_any_held() is a static inline that
>     returns !preemptible() as a proxy for "in an RCU read section".
> 
>   - On PREEMPT_RT, rcu_read_lock() does not disable preemption. A
>     task can therefore be preemptible while legitimately holding an
>     RCU read lock.
> 
>   - ath12k_wmi_tlv_rssi_chain_parse() holds the RCU read lock via
>     guard(rcu)() before calling ath12k_mac_get_arvif(), so the
>     warning is incorrect.
> 
> Typical splat seen on a WCN7850 station with periodic fw stats
> processing:
> 
>   WARNING: drivers/net/wireless/ath/ath12k/mac.c:791 at
>     ath12k_mac_get_arvif+0x9e/0xd0 [ath12k]
>   Tainted: G W O 6.19.13-rt #1 PREEMPT_RT
>   Call Trace:
>    ath12k_wmi_tlv_rssi_chain_parse+0x69/0x170 [ath12k]
>    ath12k_wmi_tlv_iter+0x7f/0x120 [ath12k]
>    ath12k_wmi_tlv_fw_stats_parse+0x342/0x6b0 [ath12k]
>    ath12k_wmi_op_rx+0xe9e/0x3150 [ath12k]
>    ath12k_htc_rx_completion_handler+0x3df/0x5b0 [ath12k]
>    ath12k_ce_per_engine_service+0x325/0x3e0 [ath12k]
>    ath12k_pci_ce_workqueue+0x20/0x40 [ath12k]
> 
> Replace the WARN_ON() with RCU_LOCKDEP_WARN(), which is gated on
> debug_lockdep_rcu_enabled() and therefore compiles out entirely
> when PROVE_RCU is disabled. PROVE_RCU kernels continue to get the
> full lockdep-based check.
> 
> Fixes: 3dd2c68f206e ("wifi: ath12k: prepare vif data structure for MLO handling")
> Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c5-00302-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.115823.3
> Signed-off-by: Yu-Hsiang Tseng <asas1asas200@gmail.com>
> ---
>  drivers/net/wireless/ath/ath12k/mac.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/ath/ath12k/mac.c b/drivers/net/wireless/ath/ath12k/mac.c
> index fbdfe6424fd7..a772a5b6adc9 100644
> --- a/drivers/net/wireless/ath/ath12k/mac.c
> +++ b/drivers/net/wireless/ath/ath12k/mac.c
> @@ -788,7 +788,8 @@ struct ath12k_link_vif *ath12k_mac_get_arvif(struct ath12k *ar, u32 vdev_id)
>  
>  	/* To use the arvif returned, caller must have held rcu read lock.
>  	 */
> -	WARN_ON(!rcu_read_lock_any_held());
> +	RCU_LOCKDEP_WARN(!rcu_read_lock_any_held(),
> +			 "RCU read lock not held");

should the instance in ath12k_p2p_noa_update_vdev_iter() also need to be replaced?

>  	arvif_iter.vdev_id = vdev_id;
>  	arvif_iter.ar = ar;
>