[PATCH] wifi: ath12k: fix race due to setting ATH12K_FLAG_EXT_IRQ_ENABLED too early

[Jeff Johnson]

On 5/23/2024 7:36 PM, Baochen Qiang wrote:
> Commit 5082b3e3027e ("wifi: ath11k: fix race due to setting
> ATH11K_FLAG_EXT_IRQ_ENABLED too early") fixes a race in ath11k
> driver. Since ath12k shares the same logic as ath11k, currently
> the race also exists in ath12k: in ath12k_pci_ext_irq_enable(),
> ATH12K_FLAG_EXT_IRQ_ENABLED is set before NAPI is enabled.
> In cases where only one MSI vector is allocated, this results
> in a race condition: after ATH12K_FLAG_EXT_IRQ_ENABLED is set
> but before NAPI enabled, CE interrupt breaks in. Since IRQ is
> shared by CE and data path, ath12k_pci_ext_interrupt_handler()
> is also called where we call disable_irq_nosync() to disable
> IRQ. Then napi_schedule() is called but it does nothing because
> NAPI is not enabled at that time, meaning that
> ath12k_pci_ext_grp_napi_poll() will never run, so we have
> no chance to call enable_irq() to enable IRQ back. Since IRQ
> is shared, all interrupts are disabled and we would finally
> get no response from target.
> 
> So port ath11k fix here, this is done by setting
> ATH12K_FLAG_EXT_IRQ_ENABLED after all NAPI and IRQ work are
> done. With the fix, we are sure that by the time
> ATH12K_FLAG_EXT_IRQ_ENABLED is set, NAPI is enabled.
> 
> Note that the fix above also introduce some side effects:
> if ath12k_pci_ext_interrupt_handler() breaks in after NAPI
> enabled but before ATH12K_FLAG_EXT_IRQ_ENABLED set, nothing
> will be done by the handler this time, the work will be
> postponed till the next time the IRQ fires.
> 
> This is found during code review.
> 
> Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3
> 
> Signed-off-by: Baochen Qiang <quic_bqiang at quicinc.com>

Acked-by: Jeff Johnson <quic_jjohnson at quicinc.com>