[PATCH] wifi: ath11k: fix race due to setting ATH11K_FLAG_EXT_IRQ_ENABLED too early

[Jeff Johnson]

On 11/16/2023 4:39 PM, Baochen Qiang wrote:
> We are seeing below error randomly in the case where only
> one MSI vector is configured:
> 
> kernel: ath11k_pci 0000:03:00.0: wmi command 16387 timeout
> 
> The reason is, currently, in ath11k_pcic_ext_irq_enable(),
> ATH11K_FLAG_EXT_IRQ_ENABLED is set before NAPI is enabled.
> This results in a race condition: after
> ATH11K_FLAG_EXT_IRQ_ENABLED is set but before NAPI enabled,
> CE interrupt breaks in. Since IRQ is shared by CE and data
> path, ath11k_pcic_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
> ath11k_pcic_ext_grp_napi_poll() will never run, so we have
> no chance to call enable_irq() to enable IRQ back. Finally
> we get above error.
> 
> Fix it by setting ATH11K_FLAG_EXT_IRQ_ENABLED after all
> NAPI and IRQ work are done. With the fix, we are sure that
> by the time ATH11K_FLAG_EXT_IRQ_ENABLED is set, NAPI is
> enabled.
> 
> Note that the fix above also introduce some side effects:
> if ath11k_pcic_ext_interrupt_handler() breaks in after NAPI
> enabled but before ATH11K_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.
> 
> Tested-on: WCN6855 hw2.1 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.23
> 
> Signed-off-by: Baochen Qiang <quic_bqiang at quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson at quicinc.com>