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

Baochen Qiang
2026-04-21T02:24:43Z

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;
>