linux-kernel - Re: [PATCH v5 1/2] bus: mhi: host: Add spinlock to protect WP access when queueing TREs

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Message-ID: <20231216051512.GA3405@thinkpad>
Date: Sat, 16 Dec 2023 10:45:12 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Qiang Yu <quic_qianyu@...cinc.com>
Cc: mani@...nel.org, quic_jhugo@...cinc.com, mhi@...ts.linux.dev,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	quic_cang@...cinc.com, quic_mrana@...cinc.com,
	Bhaumik Bhatt <bbhatt@...eaurora.org>, stable@...r.kernel.org
Subject: Re: [PATCH v5 1/2] bus: mhi: host: Add spinlock to protect WP access
 when queueing TREs

On Mon, Dec 11, 2023 at 02:42:51PM +0800, Qiang Yu wrote:
> From: Bhaumik Bhatt <bbhatt@...eaurora.org>
> 
> Protect WP accesses such that multiple threads queueing buffers for
> incoming data do not race.
> 
> Meanwhile, if CONFIG_TRACE_IRQFLAGS is enabled, irq will be enabled once
> __local_bh_enable_ip is called as part of write_unlock_bh. Hence, let's
> take irqsave lock after TRE is generated to avoid running write_unlock_bh
> when irqsave lock is held.
> 
> Cc: <stable@...r.kernel.org>
> Fixes: 189ff97cca53 ("bus: mhi: core: Add support for data transfer")
> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
> Signed-off-by: Qiang Yu <quic_qianyu@...cinc.com>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

- Mani

> ---
>  drivers/bus/mhi/host/main.c | 22 +++++++++++++---------
>  1 file changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> index dcf627b..32021fe 100644
> --- a/drivers/bus/mhi/host/main.c
> +++ b/drivers/bus/mhi/host/main.c
> @@ -1122,17 +1122,15 @@ static int mhi_queue(struct mhi_device *mhi_dev, struct mhi_buf_info *buf_info,
>  	if (unlikely(MHI_PM_IN_ERROR_STATE(mhi_cntrl->pm_state)))
>  		return -EIO;
>  
> -	read_lock_irqsave(&mhi_cntrl->pm_lock, flags);
> -
>  	ret = mhi_is_ring_full(mhi_cntrl, tre_ring);
> -	if (unlikely(ret)) {
> -		ret = -EAGAIN;
> -		goto exit_unlock;
> -	}
> +	if (unlikely(ret))
> +		return -EAGAIN;
>  
>  	ret = mhi_gen_tre(mhi_cntrl, mhi_chan, buf_info, mflags);
>  	if (unlikely(ret))
> -		goto exit_unlock;
> +		return ret;
> +
> +	read_lock_irqsave(&mhi_cntrl->pm_lock, flags);
>  
>  	/* Packet is queued, take a usage ref to exit M3 if necessary
>  	 * for host->device buffer, balanced put is done on buffer completion
> @@ -1152,7 +1150,6 @@ static int mhi_queue(struct mhi_device *mhi_dev, struct mhi_buf_info *buf_info,
>  	if (dir == DMA_FROM_DEVICE)
>  		mhi_cntrl->runtime_put(mhi_cntrl);
>  
> -exit_unlock:
>  	read_unlock_irqrestore(&mhi_cntrl->pm_lock, flags);
>  
>  	return ret;
> @@ -1204,6 +1201,9 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
>  	int eot, eob, chain, bei;
>  	int ret;
>  
> +	/* Protect accesses for reading and incrementing WP */
> +	write_lock_bh(&mhi_chan->lock);
> +
>  	buf_ring = &mhi_chan->buf_ring;
>  	tre_ring = &mhi_chan->tre_ring;
>  
> @@ -1221,8 +1221,10 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
>  
>  	if (!info->pre_mapped) {
>  		ret = mhi_cntrl->map_single(mhi_cntrl, buf_info);
> -		if (ret)
> +		if (ret) {
> +			write_unlock_bh(&mhi_chan->lock);
>  			return ret;
> +		}
>  	}
>  
>  	eob = !!(flags & MHI_EOB);
> @@ -1239,6 +1241,8 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
>  	mhi_add_ring_element(mhi_cntrl, tre_ring);
>  	mhi_add_ring_element(mhi_cntrl, buf_ring);
>  
> +	write_unlock_bh(&mhi_chan->lock);
> +
>  	return 0;
>  }
>  
> -- 
> 2.7.4
> 
> 

-- 
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