Date:   Mon, 10 Jan 2022 10:19:32 -0800
From:   Bjorn Andersson <bjorn.andersson@linaro.org>
To:     Matthias Kaehlcke <mka@chromium.org>
Cc:     Andy Gross <agross@kernel.org>, Ohad Ben-Cohen <ohad@wizery.com>,
        linux-kernel@vger.kernel.org, Sibi Sankar <sibis@codeaurora.org>,
        Sujit Kautkar <sujitka@chromium.org>,
        Stephen Boyd <swboyd@chromium.org>,
        linux-remoteproc@vger.kernel.org,
        Mathieu Poirier <mathieu.poirier@linaro.org>
Subject: Re: [PATCH v5 2/2] rpmsg: char: Fix race between the release of
 rpmsg_eptdev and cdev
Message-ID: <Ydx4tAHSfVyz2yAX@ripper>
References: <20220110091228.v5.1.Iaac908f3e3149a89190ce006ba166e2d3fd247a3@changeid>
 <20220110091228.v5.2.Idde68b05b88d4a2e6e54766c653f3a6d9e419ce6@changeid>
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In-Reply-To: <20220110091228.v5.2.Idde68b05b88d4a2e6e54766c653f3a6d9e419ce6@changeid>
Precedence: bulk

On Mon 10 Jan 09:12 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")
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> 
> Changes in v5:
> - patch added to the series
> 
>  drivers/rpmsg/rpmsg_char.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index ba85f5d11960..5bc1e6017587 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c

There's a cdev_del() in rpmsg_eptdev_release_device() that I think needs
to go as well, in line with patch 1.

Regards,
Bjorn

> @@ -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;
> @@ -380,19 +380,13 @@ 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
>