Re: [PATCH v2] wifi: ath12k: fix false positive RCU warnings on PREEMPT_RT

[Rameshkumar Sundaram]

On 4/21/2026 10:55 PM, Yu-Hsiang Tseng wrote:
> Two functions in ath12k assert that the caller holds an RCU read lock:
> ath12k_mac_get_arvif() and ath12k_p2p_noa_update_vdev_iter(). Both use:
>
>      WARN_ON(!rcu_read_lock_any_held());
>
> On PREEMPT_RT kernels built with CONFIG_PROVE_RCU=n, this produces a
> false positive splat whenever these functions are invoked from paths
> that do hold the RCU read lock (e.g. firmware stats processing or
> mac80211 interface iteration).
>
> 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.
>
>    - Callers such as ath12k_wmi_tlv_rssi_chain_parse() (via guard(rcu)())
>      and ieee80211_iterate_active_interfaces_atomic() do hold the RCU
>      read lock, so these warnings are 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
> Suggested-by: Baochen Qiang <baochen.qiang@xxxxxxxxxxxxxxxx>
> Signed-off-by: Yu-Hsiang Tseng <asas1asas200@xxxxxxxxx>
Reviewed-by: Rameshkumar Sundaram <rameshkumar.sundaram@xxxxxxxxxxxxxxxx>