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Date: Wed, 27 Jan 2021 22:03:25 +0900
From: Bongsu Jeon <bongsu.jeon2@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: shuah@...nel.org, Krzysztof Kozlowski <krzk@...nel.org>,
netdev@...r.kernel.org, linux-nfc@...ts.01.org,
linux-kselftest@...r.kernel.org,
Bongsu Jeon <bongsu.jeon@...sung.com>
Subject: Re: [PATCH net-next v3 1/2] nfc: Add a virtual nci device driver
On Wed, Jan 27, 2021 at 10:42 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Sat, 23 Jan 2021 18:24:24 +0900 Bongsu Jeon wrote:
> > From: Bongsu Jeon <bongsu.jeon@...sung.com>
> >
> > NCI virtual device simulates a NCI device to the user. It can be used to
> > validate the NCI module and applications. This driver supports
> > communication between the virtual NCI device and NCI module.
> >
> > Signed-off-by: Bongsu Jeon <bongsu.jeon@...sung.com>
>
> > +static bool virtual_ncidev_check_enabled(void)
> > +{
> > + bool ret = true;
> > +
> > + mutex_lock(&nci_mutex);
> > + if (state != virtual_ncidev_enabled)
> > + ret = false;
> > + mutex_unlock(&nci_mutex);
> > +
> > + return ret;
>
>
> This can be simplified like:
>
> bool ret;
>
> mutex_lock()
> ret = state == virtual_ncidev_enabled;
> mutex_unlock()
>
> return ret;
>
>
> > +}
> > +
> > +static int virtual_nci_open(struct nci_dev *ndev)
> > +{
> > + return 0;
> > +}
> > +
> > +static int virtual_nci_close(struct nci_dev *ndev)
> > +{
> > + mutex_lock(&nci_mutex);
> > + if (send_buff)
> > + kfree_skb(send_buff);
>
> kfree_skb() handles NULL, no need for the if, you can always call
> kfree_skb() here
>
I see, I will remove this.
> > + send_buff = NULL;
> > + mutex_unlock(&nci_mutex);
> > +
> > + return 0;
> > +}
> > +
> > +static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb)
> > +{
> > + if (virtual_ncidev_check_enabled() == false)
> > + return 0;
>
> Shouldn't you check this _under_ the lock below?
>
> Otherwise there is a small window between check and use of send_buff
>
In virtual_ncidev_check_enabled function, mutex is used.
I think that virtual_ncidev_check_enabled function isn't necessary
after refactoring.
So I'll remove it.
> > + mutex_lock(&nci_mutex);
> > + if (send_buff) {
> > + mutex_unlock(&nci_mutex);
> > + return -1;
> > + }
> > + send_buff = skb_copy(skb, GFP_KERNEL);
> > + mutex_unlock(&nci_mutex);
> > +
> > + return 0;
> > +}
> > +
> > +static struct nci_ops virtual_nci_ops = {
> > + .open = virtual_nci_open,
> > + .close = virtual_nci_close,
> > + .send = virtual_nci_send
> > +};
> > +
> > +static ssize_t virtual_ncidev_read(struct file *file, char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + size_t actual_len;
> > +
> > + mutex_lock(&nci_mutex);
> > + if (!send_buff) {
> > + mutex_unlock(&nci_mutex);
> > + return 0;
> > + }
> > +
> > + actual_len = min_t(size_t, count, send_buff->len);
> > +
> > + if (copy_to_user(buf, send_buff->data, actual_len)) {
> > + mutex_unlock(&nci_mutex);
> > + return -EFAULT;
> > + }
> > +
> > + skb_pull(send_buff, actual_len);
> > + if (send_buff->len == 0) {
> > + consume_skb(send_buff);
> > + send_buff = NULL;
> > + }
> > + mutex_unlock(&nci_mutex);
> > +
> > + return actual_len;
> > +}
> > +
> > +static ssize_t virtual_ncidev_write(struct file *file,
> > + const char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + struct sk_buff *skb;
> > +
> > + skb = alloc_skb(count, GFP_KERNEL);
> > + if (!skb)
> > + return -ENOMEM;
> > +
> > + if (copy_from_user(skb_put(skb, count), buf, count)) {
> > + kfree_skb(skb);
> > + return -EFAULT;
> > + }
> > +
> > + nci_recv_frame(ndev, skb);
> > + return count;
> > +}
> > +
> > +static int virtual_ncidev_open(struct inode *inode, struct file *file)
> > +{
> > + int ret = 0;
> > +
> > + mutex_lock(&nci_mutex);
> > + if (state != virtual_ncidev_disabled) {
> > + mutex_unlock(&nci_mutex);
> > + return -EBUSY;
> > + }
> > +
> > + ndev = nci_allocate_device(&virtual_nci_ops, VIRTUAL_NFC_PROTOCOLS,
> > + 0, 0);
> > + if (!ndev) {
> > + mutex_unlock(&nci_mutex);
> > + return -ENOMEM;
> > + }
> > +
> > + ret = nci_register_device(ndev);
> > + if (ret < 0) {
> > + nci_free_device(ndev);
> > + mutex_unlock(&nci_mutex);
> > + return ret;
> > + }
> > + state = virtual_ncidev_enabled;
> > + mutex_unlock(&nci_mutex);
> > +
> > + return 0;
> > +}
> > +
> > +static int virtual_ncidev_close(struct inode *inode, struct file *file)
> > +{
> > + mutex_lock(&nci_mutex);
> > +
> > + if (state == virtual_ncidev_enabled) {
> > + state = virtual_ncidev_disabling;
> > + mutex_unlock(&nci_mutex);
> > +
> > + nci_unregister_device(ndev);
> > + nci_free_device(ndev);
> > +
> > + mutex_lock(&nci_mutex);
> > + }
> > +
> > + state = virtual_ncidev_disabled;
> > + mutex_unlock(&nci_mutex);
> > +
> > + return 0;
> > +}
> > +
> > +static long virtual_ncidev_ioctl(struct file *flip, unsigned int cmd,
> > + unsigned long arg)
> > +{
> > + if (cmd == IOCTL_GET_NCIDEV_IDX) {
> > + struct nfc_dev *nfc_dev = ndev->nfc_dev;
> > + void __user *p = (void __user *)arg;
> > +
> > + if (copy_to_user(p, &nfc_dev->idx, sizeof(nfc_dev->idx)))
> > + return -EFAULT;
> > + } else {
> > + return -ENOTTY;
> > + }
> > +
> > + return 0;
>
> Please flip the condition and return early. I think I suggested this
> already:
Sorry, I didn't misunderstand it.
I will change it.
>
> {
> struct nfc_dev *nfc_dev = ndev->nfc_dev;
> void __user *p = (void __user *)arg;
>
> if (cmd != IOCTL_GET_NCIDEV_IDX)
> return -ENOTTY;
>
> if (copy_to_user(p, &nfc_dev->idx, sizeof(nfc_dev->idx)))
> return -EFAULT;
>
> return 0;
Thank you for your review.
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