linux-kernel - Re: [RESEND PATCH] rpmsg: char: Add mutex protection for rpmsg_eptdev

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Date:   Tue, 31 May 2022 11:28:43 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Shengjiu Wang <shengjiu.wang@....com>
Cc:     bjorn.andersson@...aro.org, arnaud.pouliquen@...s.st.com,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        shengjiu.wang@...il.com
Subject: Re: [RESEND PATCH] rpmsg: char: Add mutex protection for
 rpmsg_eptdev_open()

On Sat, May 21, 2022 at 11:35:05AM +0800, Shengjiu Wang wrote:
> There is no mutex protection for rpmsg_eptdev_open(),
> especially for eptdev->ept read and write operation.
> It may cause issues when multiple instances call
> rpmsg_eptdev_open() in parallel,the return state
> may be success or EBUGY.
> 
> Fixes: 964e8bedd5a1 ("rpmsg: char: Return an error if device already open")
> Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>

This looks good.  I will fix the above typo and apply the patch when the 5.19 cycle
starts.

Thanks,
Mathieu

> ---
> changes in resend:
> - add fixes tag
> 
>  drivers/rpmsg/rpmsg_char.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index b6183d4f62a2..4f2189111494 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c
> @@ -120,8 +120,11 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
>  	struct rpmsg_device *rpdev = eptdev->rpdev;
>  	struct device *dev = &eptdev->dev;
>  
> -	if (eptdev->ept)
> +	mutex_lock(&eptdev->ept_lock);
> +	if (eptdev->ept) {
> +		mutex_unlock(&eptdev->ept_lock);
>  		return -EBUSY;
> +	}
>  
>  	get_device(dev);
>  
> @@ -137,11 +140,13 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
>  	if (!ept) {
>  		dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
>  		put_device(dev);
> +		mutex_unlock(&eptdev->ept_lock);
>  		return -EINVAL;
>  	}
>  
>  	eptdev->ept = ept;
>  	filp->private_data = eptdev;
> +	mutex_unlock(&eptdev->ept_lock);
>  
>  	return 0;
>  }
> -- 
> 2.17.1
>