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Date:   Sat, 11 Jan 2020 20:40:06 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Zhangfei Gao <zhangfei.gao@linaro.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        jonathan.cameron@huawei.com, dave.jiang@intel.com,
        grant.likely@arm.com, jean-philippe <jean-philippe@linaro.org>,
        Jerome Glisse <jglisse@redhat.com>,
        ilias.apalodimas@linaro.org, francois.ozog@linaro.org,
        kenneth-lee-2012@foxmail.com, Wangzhou <wangzhou1@hisilicon.com>,
        "haojian . zhuang" <haojian.zhuang@linaro.org>,
        guodong.xu@linaro.org, linux-accelerators@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        iommu@lists.linux-foundation.org,
        Kenneth Lee <liguozhu@hisilicon.com>,
        Zaibo Xu <xuzaibo@huawei.com>
Subject: Re: [PATCH v11 2/4] uacce: add uacce driver
Message-ID: <20200111194006.GD435222@kroah.com>
References: <1578710919-12141-1-git-send-email-zhangfei.gao@linaro.org>
 <1578710919-12141-3-git-send-email-zhangfei.gao@linaro.org>
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On Sat, Jan 11, 2020 at 10:48:37AM +0800, Zhangfei Gao wrote:
> +static int uacce_fops_open(struct inode *inode, struct file *filep)
> +{
> +	struct uacce_mm *uacce_mm = NULL;
> +	struct uacce_device *uacce;
> +	struct uacce_queue *q;
> +	int ret = 0;
> +
> +	uacce = xa_load(&uacce_xa, iminor(inode));
> +	if (!uacce)
> +		return -ENODEV;
> +
> +	if (!try_module_get(uacce->parent->driver->owner))
> +		return -ENODEV;

Why are you trying to grab the module reference of the parent device?
Why is that needed and what is that going to help with here?

This shouldn't be needed as the module reference of the owner of the
fileops for this module is incremented, and the "parent" module depends
on this module, so how could it be unloaded without this code being
unloaded?

Yes, if you build this code into the kernel and the "parent" driver is a
module, then you will not have a reference, but when you remove that
parent driver the device will be removed as it has to be unregistered
before that parent driver can be removed from the system, right?

Or what am I missing here?

> +static void uacce_release(struct device *dev)
> +{
> +	struct uacce_device *uacce = to_uacce_device(dev);
> +
> +	kfree(uacce);
> +	uacce = NULL;

That line didn't do anything :)

thanks,

greg k-h