linux-kernel - Re: [PATCH v3] bus: mhi: host: Disable preemption while processing data events

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Message-ID: <20221117114923.GD93179@thinkpad>
Date:   Thu, 17 Nov 2022 17:19:23 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Qiang Yu <quic_qianyu@...cinc.com>
Cc:     mani@...nel.org, loic.poulain@...aro.org, 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 v3] bus: mhi: host: Disable preemption while processing
 data events

On Tue, Nov 15, 2022 at 10:23:51AM +0800, 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>
> ---
> v2->v3: modify the comment
> 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..5dca0a0 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;

Reverse X-Mas tree order please. Move this definition to the last.

>  	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 multiple IRQs come, the tasklet will be scheduled out with event ring lock

s/come/arrive

> +	 * remaining acquired, causing M0 event process on another core gets stuck when it

s/remaining//

"causing other high priority events like M0 state transition getting stuck
while trying to acquire the same event ring lock."

> +	 * tries to acquire the same event ring lock. Thus, let's disable local IRQs here.
> +	 */

This comment should be placed above spin_lock_irqsave().

The comment "process all pending events" can be moved here.

Thanks,
Mani

> +
>  	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)
> -- 
> 2.7.4
> 
> 

-- 
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