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4498664e2d
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 kernels using preemptible RCU (CONFIG_PREEMPT=y or CONFIG_PREEMPT_RT=y)
without CONFIG_DEBUG_LOCK_ALLOC, 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:
- Without CONFIG_DEBUG_LOCK_ALLOC, rcu_read_lock_any_held() is a
static inline that returns !preemptible() as a proxy for "in an
RCU read section".
- With preemptible RCU, rcu_read_lock() does not disable preemption.
A task can therefore be preemptible while legitimately holding an
RCU read lock, making the proxy unreliable.
- 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 WARN_ON(!rcu_read_lock_any_held()) with
lockdep_assert_in_rcu_read_lock(), which is gated on CONFIG_PROVE_RCU
and therefore compiles out entirely when PROVE_RCU is disabled.
PROVE_RCU kernels continue to get the full lockdep-based check, and
the new helper precisely checks for rcu_read_lock() rather than any
RCU variant, which better matches the callers' expectations.
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c5-00302-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.115823.3
Fixes:
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History
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