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

[Yu-Hsiang Tseng]

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 at 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");
 	arvif_iter.vdev_id = vdev_id;
 	arvif_iter.ar = ar;
 
-- 
2.53.0