linux-kernel - Re: [PATCH v2] bus: mhi: host: Disable preemption while processing data events

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Message-ID: <8aae17cf-7c2b-85bb-d0f5-a5f71e792d16@quicinc.com>
Date:   Mon, 14 Nov 2022 07:53:28 -0700
From:   Jeffrey Hugo <quic_jhugo@...cinc.com>
To:     Qiang Yu <quic_qianyu@...cinc.com>, <mani@...nel.org>,
        <loic.poulain@...aro.org>
CC:     <mhi@...ts.linux.dev>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_cang@...cinc.com>,
        <mrana@...cinc.com>
Subject: Re: [PATCH v2] bus: mhi: host: Disable preemption while processing
 data events

On 11/14/2022 2:58 AM, Qiang Yu wrote:
> If data processing of an event is scheduled out because core
> is busy handling multiple irqs, this can starve the processing
> of MHI M0 state change event on another core. Fix this issue by
> disabling irq on the core processing data events.
> 
> Signed-off-by: Qiang Yu <quic_qianyu@...cinc.com>
> ---
> v1->v2: add comments about why we disable local irq
> 
>   drivers/bus/mhi/host/main.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> index f3aef77a..fcb2586 100644
> --- a/drivers/bus/mhi/host/main.c
> +++ b/drivers/bus/mhi/host/main.c
> @@ -1027,13 +1027,20 @@ int mhi_process_data_event_ring(struct mhi_controller *mhi_cntrl,
>   
>   void mhi_ev_task(unsigned long data)
>   {
> +	unsigned long flags;
>   	struct mhi_event *mhi_event = (struct mhi_event *)data;
>   	struct mhi_controller *mhi_cntrl = mhi_event->mhi_cntrl;
>   
>   	/* process all pending events */
> -	spin_lock_bh(&mhi_event->lock);
> +	spin_lock_irqsave(&mhi_event->lock, flags);
> +	/*
> +	 * When muiltiple IRQs come, the tasklet will be scheduled out with event ring lock

multiple

> +	 * remaining acquired, causing M0 event process on another core gets stuck when it
> +	 * tries to acquire the same event ring lock. Thus let's disable local IRQs here.
> +	 */
> +
>   	mhi_event->process_event(mhi_cntrl, mhi_event, U32_MAX);
> -	spin_unlock_bh(&mhi_event->lock);
> +	spin_unlock_irqrestore(&mhi_event->lock, flags);
>   }
>   
>   void mhi_ctrl_ev_task(unsigned long data)