linux-kernel - Re: [PATCH v2 1/2] bus: mhi: host: Add spinlock to protect WP access when queueing TREs

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Date:   Mon, 6 Nov 2023 10:11:26 +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>
Subject: Re: [PATCH v2 1/2] bus: mhi: host: Add spinlock to protect WP access
 when queueing TREs

On Wed, Sep 13, 2023 at 04:47:40PM +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 and access the same WP twice. Ensure read and
> write locks for the channel are not taken in succession by dropping the
> read lock from parse_xfer_event() such that a callback given to client
> can potentially queue buffers and acquire the write lock in that process.
> Any queueing of buffers should be done without channel read lock acquired
> as it can result in multiple locks and a soft lockup.
> 

This change is doing two things:

1. Unlocking xfer_cb to prevent potential lockup
2. Protecting mhi_gen_tre() against concurrent access

So you should split this into two patches and also add Fixes tag if appropriate.

- Mani

> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
> Signed-off-by: Qiang Yu <quic_qianyu@...cinc.com>
> ---
>  drivers/bus/mhi/host/main.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> index dcf627b..13c4b89 100644
> --- a/drivers/bus/mhi/host/main.c
> +++ b/drivers/bus/mhi/host/main.c
> @@ -642,6 +642,7 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
>  			mhi_del_ring_element(mhi_cntrl, tre_ring);
>  			local_rp = tre_ring->rp;
>  
> +			read_unlock_bh(&mhi_chan->lock);
>  			/* notify client */
>  			mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
>  
> @@ -667,6 +668,7 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
>  					kfree(buf_info->cb_buf);
>  				}
>  			}
> +			read_lock_bh(&mhi_chan->lock);
>  		}
>  		break;
>  	} /* CC_EOT */
> @@ -1204,6 +1206,9 @@ 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 +1226,10 @@ 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 +1246,8 @@ 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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