linux-kernel - Re: [PATCH v6 2/2] rpmsg: char: Fix race between the release of rpmsg

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Date:   Mon, 10 Jan 2022 10:56:03 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Andy Gross <agross@...nel.org>, Ohad Ben-Cohen <ohad@...ery.com>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        Sibi Sankar <sibis@...eaurora.org>,
        Sujit Kautkar <sujitka@...omium.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH v6 2/2] rpmsg: char: Fix race between the release of
 rpmsg_eptdev and cdev

On Mon 10 Jan 10:47 PST 2022, Matthias Kaehlcke wrote:

> struct rpmsg_eptdev contains a struct cdev. The current code frees
> the rpmsg_eptdev struct in rpmsg_eptdev_destroy(), but the cdev is
> a managed object, therefore its release is not predictable and the
> rpmsg_eptdev could be freed before the cdev is entirely released.
> 
> The cdev_device_add/del() API was created to address this issue
> (see commit 233ed09d7fda), use it instead of cdev add/del().
> 
> Fixes: c0cdc19f84a4 ("rpmsg: Driver for user space endpoint interface")
> Suggested-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> ---
> 
> Changes in v6:
> - remove cdev_del() from rpmsg_eptdev_release_device()
> - added 'Reviewed-by' tag from Mathieu and 'Suggested-by' tag
> 
> Changes in v5:
> - patch added to the series
> 
>  drivers/rpmsg/rpmsg_char.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index ba85f5d11960..49dd5a200998 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c
> @@ -92,7 +92,7 @@ static int rpmsg_eptdev_destroy(struct device *dev, void *data)
>  	/* wake up any blocked readers */
>  	wake_up_interruptible(&eptdev->readq);
>  
> -	device_del(&eptdev->dev);
> +	cdev_device_del(&eptdev->cdev, &eptdev->dev);
>  	put_device(&eptdev->dev);
>  
>  	return 0;
> @@ -335,7 +335,6 @@ static void rpmsg_eptdev_release_device(struct device *dev)
>  
>  	ida_simple_remove(&rpmsg_ept_ida, dev->id);
>  	ida_simple_remove(&rpmsg_minor_ida, MINOR(eptdev->dev.devt));
> -	cdev_del(&eptdev->cdev);
>  	kfree(eptdev);
>  }
>  
> @@ -380,19 +379,13 @@ static int rpmsg_eptdev_create(struct rpmsg_ctrldev *ctrldev,
>  	dev->id = ret;
>  	dev_set_name(dev, "rpmsg%d", ret);
>  
> -	ret = cdev_add(&eptdev->cdev, dev->devt, 1);
> +	ret = cdev_device_add(&eptdev->cdev, &eptdev->dev);
>  	if (ret)
>  		goto free_ept_ida;
>  
>  	/* We can now rely on the release function for cleanup */
>  	dev->release = rpmsg_eptdev_release_device;
>  
> -	ret = device_add(dev);
> -	if (ret) {
> -		dev_err(dev, "device_add failed: %d\n", ret);
> -		put_device(dev);
> -	}
> -
>  	return ret;
>  
>  free_ept_ida:
> -- 
> 2.34.1.575.g55b058a8bb-goog
>