diff mbox series

[4/4] gpiolib: cdev: replace locking wrappers for gpio_device with guards

Message ID 20231220015106.16732-5-warthog618@gmail.com
State New
Headers show
Series gpiolib: cdev: guard tidying | expand

Commit Message

Kent Gibson Dec. 20, 2023, 1:51 a.m. UTC 
Replace the wrapping functions that inhibit removal of the gpio_device
with equivalent guard macros.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
---
 drivers/gpio/gpiolib-cdev.c | 195 ++++++++++--------------------------
 1 file changed, 52 insertions(+), 143 deletions(-)

Comments

Bartosz Golaszewski Dec. 20, 2023, 12:05 p.m. UTC | #1 
On Wed, Dec 20, 2023 at 12:56 PM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> (+PeterZ)
>
> On Wed, Dec 20, 2023 at 2:52 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> > Replace the wrapping functions that inhibit removal of the gpio_device
> > with equivalent guard macros.
> >
> > Signed-off-by: Kent Gibson <warthog618@gmail.com>
> (...)
> > +DEFINE_CLASS(_read_sem_guard,
> > +            struct rw_semaphore *,
> > +            up_read(_T),
> > +            ({
> > +               down_read(sem);
> > +               sem;
> > +            }),
> > +            struct rw_semaphore *sem);
>
> Isn't this so generic that it should be in <linux/cleanup.h>?
>
> Otherwise all the patches look good to me.
>

We already have this:

DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T))
DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T))

DEFINE_FREE(up_read, struct rw_semaphore *, if (_T) up_read(_T))
DEFINE_FREE(up_write, struct rw_semaphore *, if (_T) up_write(_T))

This can surely be used here, right?

Bart

> Yours,
> Linus Walleij
Bartosz Golaszewski Dec. 20, 2023, 12:16 p.m. UTC | #2 
On Wed, Dec 20, 2023 at 1:13 PM Kent Gibson <warthog618@gmail.com> wrote:
>
> On Wed, Dec 20, 2023 at 01:05:35PM +0100, Bartosz Golaszewski wrote:
> > On Wed, Dec 20, 2023 at 12:56 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> > >
> > > (+PeterZ)
> > >
> > > On Wed, Dec 20, 2023 at 2:52 AM Kent Gibson <warthog618@gmail.com> wrote:
> > >
> > > > Replace the wrapping functions that inhibit removal of the gpio_device
> > > > with equivalent guard macros.
> > > >
> > > > Signed-off-by: Kent Gibson <warthog618@gmail.com>
> > > (...)
> > > > +DEFINE_CLASS(_read_sem_guard,
> > > > +            struct rw_semaphore *,
> > > > +            up_read(_T),
> > > > +            ({
> > > > +               down_read(sem);
> > > > +               sem;
> > > > +            }),
> > > > +            struct rw_semaphore *sem);
> > >
> > > Isn't this so generic that it should be in <linux/cleanup.h>?
> > >
> > > Otherwise all the patches look good to me.
> > >
> >
> > We already have this:
> >
> > DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T))
> > DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T))
> >
> > DEFINE_FREE(up_read, struct rw_semaphore *, if (_T) up_read(_T))
> > DEFINE_FREE(up_write, struct rw_semaphore *, if (_T) up_write(_T))
> >
>
> Ah - in rwsem.h - I missed that.
>
> > This can surely be used here, right?
> >
>
> Don't see why not.
>
> I would still like to move the gpio_device specific macros to gpiolib.h,
> as they apply to the struct gpio_device defined there.

Which ones? Because I'd rather use guard(rwsem_read)(&gdev->sem); than
some custom wrapper as this one's purpose is clearer.

Bart

> The naming probably needs some reworking, so open to suggestions on
> that.
>
> Cheers,
> Kent.
Kent Gibson Dec. 20, 2023, 12:53 p.m. UTC | #3 
On Wed, Dec 20, 2023 at 01:30:57PM +0100, Bartosz Golaszewski wrote:
> On Wed, Dec 20, 2023 at 1:23 PM Kent Gibson <warthog618@gmail.com> wrote:
> >
> > >
> >
> > It would be read and write guards for the gpio_device.
> > cdev would only be using the read flavour.
> > And possibly named something other than read/write as the purpose is to
> > prevent (read) or allow (write) object removal.
> >
> > I though that would be clearer than having to reference gpiolib.h to see
> > what gdev->sem covers, and allow you to change the locking
> > mechanism later and not have to update cdev.
> >
>
> I still prefer open-coded guards here for clarity. I hope that with
> SRCU in gpiolib.c, we'll get rid of locking in cdev entirely anyway.
>

Ok, it is your object so I should use it the way you want it used.

Btw, before I go pushing out a v2, do you have an answer on whether
gpio_ioctl() requires a guard, as mentioned in the cover letter?
Is the fact there is an active ioctl on the chardev sufficient in
itself to keep the gpio_device alive?

Cheers,
Kent.
Kent Gibson Dec. 20, 2023, 1:28 p.m. UTC | #4 
On Wed, Dec 20, 2023 at 02:19:37PM +0100, Bartosz Golaszewski wrote:
> On Wed, Dec 20, 2023 at 1:53 PM Kent Gibson <warthog618@gmail.com> wrote:
> >
> > On Wed, Dec 20, 2023 at 01:30:57PM +0100, Bartosz Golaszewski wrote:
> > > On Wed, Dec 20, 2023 at 1:23 PM Kent Gibson <warthog618@gmail.com> wrote:
> > > >
> > > > >
> > > >
> > > > It would be read and write guards for the gpio_device.
> > > > cdev would only be using the read flavour.
> > > > And possibly named something other than read/write as the purpose is to
> > > > prevent (read) or allow (write) object removal.
> > > >
> > > > I though that would be clearer than having to reference gpiolib.h to see
> > > > what gdev->sem covers, and allow you to change the locking
> > > > mechanism later and not have to update cdev.
> > > >
> > >
> > > I still prefer open-coded guards here for clarity. I hope that with
> > > SRCU in gpiolib.c, we'll get rid of locking in cdev entirely anyway.
> > >
> >
> > Ok, it is your object so I should use it the way you want it used.
> >
> > Btw, before I go pushing out a v2, do you have an answer on whether
> > gpio_ioctl() requires a guard, as mentioned in the cover letter?
> > Is the fact there is an active ioctl on the chardev sufficient in
> > itself to keep the gpio_device alive?
> >
>
> AFAICT: no. I think it's a bug (good catch!).

The wrappers made that harder to pick up.
It kind of stood out as the exception after changing the other ioctls
over to guards - where was the guard for that one?

> Can you extend your
> series with a backportable bugfix that would come first?
>

Sure.  That would still use the guard(rwsem_read)?
I mean you don't to go adding a wrapper for the fix, just to
subsequently remove it, right?

Cheers,
Kent.
diff mbox series

Patch

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 5b07578e3bfa..77ecf308ef39 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -65,44 +65,20 @@  typedef long (*ioctl_fn)(struct file *, unsigned int, unsigned long);
 typedef ssize_t (*read_fn)(struct file *, char __user *,
 			   size_t count, loff_t *);
 
-static __poll_t call_poll_locked(struct file *file,
-				 struct poll_table_struct *wait,
-				 struct gpio_device *gdev, poll_fn func)
-{
-	__poll_t ret;
-
-	down_read(&gdev->sem);
-	ret = func(file, wait);
-	up_read(&gdev->sem);
-
-	return ret;
-}
-
-static long call_ioctl_locked(struct file *file, unsigned int cmd,
-			      unsigned long arg, struct gpio_device *gdev,
-			      ioctl_fn func)
-{
-	long ret;
+DEFINE_CLASS(_read_sem_guard,
+	     struct rw_semaphore *,
+	     up_read(_T),
+	     ({
+		down_read(sem);
+		sem;
+	     }),
+	     struct rw_semaphore *sem);
 
-	down_read(&gdev->sem);
-	ret = func(file, cmd, arg);
-	up_read(&gdev->sem);
+/* guard that downs a rw_semaphore while in scope */
+#define read_sem_guard(sem) CLASS(_read_sem_guard, _sem)(sem)
 
-	return ret;
-}
-
-static ssize_t call_read_locked(struct file *file, char __user *buf,
-				size_t count, loff_t *f_ps,
-				struct gpio_device *gdev, read_fn func)
-{
-	ssize_t ret;
-
-	down_read(&gdev->sem);
-	ret = func(file, buf, count, f_ps);
-	up_read(&gdev->sem);
-
-	return ret;
-}
+/* guard on the gpio_device sem to inhibit device removal while in use */
+#define gdev_guard(gdev) read_sem_guard(gdev->sem)
 
 /*
  * GPIO line handle management
@@ -238,8 +214,8 @@  static long linehandle_set_config(struct linehandle_state *lh,
 	return 0;
 }
 
-static long linehandle_ioctl_unlocked(struct file *file, unsigned int cmd,
-				      unsigned long arg)
+static long linehandle_ioctl(struct file *file, unsigned int cmd,
+			     unsigned long arg)
 {
 	struct linehandle_state *lh = file->private_data;
 	void __user *ip = (void __user *)arg;
@@ -248,6 +224,8 @@  static long linehandle_ioctl_unlocked(struct file *file, unsigned int cmd,
 	unsigned int i;
 	int ret;
 
+	gdev_guard(&lh->gdev);
+
 	if (!lh->gdev->chip)
 		return -ENODEV;
 
@@ -297,15 +275,6 @@  static long linehandle_ioctl_unlocked(struct file *file, unsigned int cmd,
 	}
 }
 
-static long linehandle_ioctl(struct file *file, unsigned int cmd,
-			     unsigned long arg)
-{
-	struct linehandle_state *lh = file->private_data;
-
-	return call_ioctl_locked(file, cmd, arg, lh->gdev,
-				 linehandle_ioctl_unlocked);
-}
-
 #ifdef CONFIG_COMPAT
 static long linehandle_ioctl_compat(struct file *file, unsigned int cmd,
 				    unsigned long arg)
@@ -1564,12 +1533,14 @@  static long linereq_set_config(struct linereq *lr, void __user *ip)
 	return 0;
 }
 
-static long linereq_ioctl_unlocked(struct file *file, unsigned int cmd,
-				   unsigned long arg)
+static long linereq_ioctl(struct file *file, unsigned int cmd,
+			  unsigned long arg)
 {
 	struct linereq *lr = file->private_data;
 	void __user *ip = (void __user *)arg;
 
+	gdev_guard(&lr->gdev);
+
 	if (!lr->gdev->chip)
 		return -ENODEV;
 
@@ -1585,15 +1556,6 @@  static long linereq_ioctl_unlocked(struct file *file, unsigned int cmd,
 	}
 }
 
-static long linereq_ioctl(struct file *file, unsigned int cmd,
-			  unsigned long arg)
-{
-	struct linereq *lr = file->private_data;
-
-	return call_ioctl_locked(file, cmd, arg, lr->gdev,
-				 linereq_ioctl_unlocked);
-}
-
 #ifdef CONFIG_COMPAT
 static long linereq_ioctl_compat(struct file *file, unsigned int cmd,
 				 unsigned long arg)
@@ -1602,12 +1564,14 @@  static long linereq_ioctl_compat(struct file *file, unsigned int cmd,
 }
 #endif
 
-static __poll_t linereq_poll_unlocked(struct file *file,
-				      struct poll_table_struct *wait)
+static __poll_t linereq_poll(struct file *file,
+			     struct poll_table_struct *wait)
 {
 	struct linereq *lr = file->private_data;
 	__poll_t events = 0;
 
+	gdev_guard(&lr->gdev);
+
 	if (!lr->gdev->chip)
 		return EPOLLHUP | EPOLLERR;
 
@@ -1620,22 +1584,16 @@  static __poll_t linereq_poll_unlocked(struct file *file,
 	return events;
 }
 
-static __poll_t linereq_poll(struct file *file,
-			     struct poll_table_struct *wait)
-{
-	struct linereq *lr = file->private_data;
-
-	return call_poll_locked(file, wait, lr->gdev, linereq_poll_unlocked);
-}
-
-static ssize_t linereq_read_unlocked(struct file *file, char __user *buf,
-				     size_t count, loff_t *f_ps)
+static ssize_t linereq_read(struct file *file, char __user *buf,
+			    size_t count, loff_t *f_ps)
 {
 	struct linereq *lr = file->private_data;
 	struct gpio_v2_line_event le;
 	ssize_t bytes_read = 0;
 	int ret;
 
+	gdev_guard(&lr->gdev);
+
 	if (!lr->gdev->chip)
 		return -ENODEV;
 
@@ -1677,15 +1635,6 @@  static ssize_t linereq_read_unlocked(struct file *file, char __user *buf,
 	return bytes_read;
 }
 
-static ssize_t linereq_read(struct file *file, char __user *buf,
-			    size_t count, loff_t *f_ps)
-{
-	struct linereq *lr = file->private_data;
-
-	return call_read_locked(file, buf, count, f_ps, lr->gdev,
-				linereq_read_unlocked);
-}
-
 static void linereq_free(struct linereq *lr)
 {
 	struct line *line;
@@ -1938,12 +1887,14 @@  struct lineevent_state {
 	(GPIOEVENT_REQUEST_RISING_EDGE | \
 	GPIOEVENT_REQUEST_FALLING_EDGE)
 
-static __poll_t lineevent_poll_unlocked(struct file *file,
-					struct poll_table_struct *wait)
+static __poll_t lineevent_poll(struct file *file,
+			       struct poll_table_struct *wait)
 {
 	struct lineevent_state *le = file->private_data;
 	__poll_t events = 0;
 
+	gdev_guard(&le->gdev);
+
 	if (!le->gdev->chip)
 		return EPOLLHUP | EPOLLERR;
 
@@ -1955,14 +1906,6 @@  static __poll_t lineevent_poll_unlocked(struct file *file,
 	return events;
 }
 
-static __poll_t lineevent_poll(struct file *file,
-			       struct poll_table_struct *wait)
-{
-	struct lineevent_state *le = file->private_data;
-
-	return call_poll_locked(file, wait, le->gdev, lineevent_poll_unlocked);
-}
-
 static int lineevent_unregistered_notify(struct notifier_block *nb,
 					 unsigned long action, void *data)
 {
@@ -1979,8 +1922,8 @@  struct compat_gpioeevent_data {
 	u32		id;
 };
 
-static ssize_t lineevent_read_unlocked(struct file *file, char __user *buf,
-				       size_t count, loff_t *f_ps)
+static ssize_t lineevent_read(struct file *file, char __user *buf,
+			      size_t count, loff_t *f_ps)
 {
 	struct lineevent_state *le = file->private_data;
 	struct gpioevent_data ge;
@@ -1988,6 +1931,8 @@  static ssize_t lineevent_read_unlocked(struct file *file, char __user *buf,
 	ssize_t ge_size;
 	int ret;
 
+	gdev_guard(&le->gdev);
+
 	if (!le->gdev->chip)
 		return -ENODEV;
 
@@ -2042,15 +1987,6 @@  static ssize_t lineevent_read_unlocked(struct file *file, char __user *buf,
 	return bytes_read;
 }
 
-static ssize_t lineevent_read(struct file *file, char __user *buf,
-			      size_t count, loff_t *f_ps)
-{
-	struct lineevent_state *le = file->private_data;
-
-	return call_read_locked(file, buf, count, f_ps, le->gdev,
-				lineevent_read_unlocked);
-}
-
 static void lineevent_free(struct lineevent_state *le)
 {
 	if (le->device_unregistered_nb.notifier_call)
@@ -2071,13 +2007,15 @@  static int lineevent_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
-static long lineevent_ioctl_unlocked(struct file *file, unsigned int cmd,
-				     unsigned long arg)
+static long lineevent_ioctl(struct file *file, unsigned int cmd,
+			    unsigned long arg)
 {
 	struct lineevent_state *le = file->private_data;
 	void __user *ip = (void __user *)arg;
 	struct gpiohandle_data ghd;
 
+	gdev_guard(&le->gdev);
+
 	if (!le->gdev->chip)
 		return -ENODEV;
 
@@ -2103,15 +2041,6 @@  static long lineevent_ioctl_unlocked(struct file *file, unsigned int cmd,
 	return -EINVAL;
 }
 
-static long lineevent_ioctl(struct file *file, unsigned int cmd,
-			    unsigned long arg)
-{
-	struct lineevent_state *le = file->private_data;
-
-	return call_ioctl_locked(file, cmd, arg, le->gdev,
-				 lineevent_ioctl_unlocked);
-}
-
 #ifdef CONFIG_COMPAT
 static long lineevent_ioctl_compat(struct file *file, unsigned int cmd,
 				   unsigned long arg)
@@ -2671,12 +2600,14 @@  static int gpio_device_unregistered_notify(struct notifier_block *nb,
 	return NOTIFY_OK;
 }
 
-static __poll_t lineinfo_watch_poll_unlocked(struct file *file,
-					     struct poll_table_struct *pollt)
+static __poll_t lineinfo_watch_poll(struct file *file,
+				    struct poll_table_struct *pollt)
 {
 	struct gpio_chardev_data *cdev = file->private_data;
 	__poll_t events = 0;
 
+	gdev_guard(&cdev->gdev);
+
 	if (!cdev->gdev->chip)
 		return EPOLLHUP | EPOLLERR;
 
@@ -2689,17 +2620,8 @@  static __poll_t lineinfo_watch_poll_unlocked(struct file *file,
 	return events;
 }
 
-static __poll_t lineinfo_watch_poll(struct file *file,
-				    struct poll_table_struct *pollt)
-{
-	struct gpio_chardev_data *cdev = file->private_data;
-
-	return call_poll_locked(file, pollt, cdev->gdev,
-				lineinfo_watch_poll_unlocked);
-}
-
-static ssize_t lineinfo_watch_read_unlocked(struct file *file, char __user *buf,
-					    size_t count, loff_t *off)
+static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
+				   size_t count, loff_t *off)
 {
 	struct gpio_chardev_data *cdev = file->private_data;
 	struct gpio_v2_line_info_changed event;
@@ -2707,6 +2629,8 @@  static ssize_t lineinfo_watch_read_unlocked(struct file *file, char __user *buf,
 	int ret;
 	size_t event_size;
 
+	gdev_guard(&cdev->gdev);
+
 	if (!cdev->gdev->chip)
 		return -ENODEV;
 
@@ -2769,15 +2693,6 @@  static ssize_t lineinfo_watch_read_unlocked(struct file *file, char __user *buf,
 	return bytes_read;
 }
 
-static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
-				   size_t count, loff_t *off)
-{
-	struct gpio_chardev_data *cdev = file->private_data;
-
-	return call_read_locked(file, buf, count, off, cdev->gdev,
-				lineinfo_watch_read_unlocked);
-}
-
 /**
  * gpio_chrdev_open() - open the chardev for ioctl operations
  * @inode: inode for this chardev
@@ -2791,17 +2706,15 @@  static int gpio_chrdev_open(struct inode *inode, struct file *file)
 	struct gpio_chardev_data *cdev;
 	int ret = -ENOMEM;
 
-	down_read(&gdev->sem);
+	gdev_guard(&gdev);
 
 	/* Fail on open if the backing gpiochip is gone */
-	if (!gdev->chip) {
-		ret = -ENODEV;
-		goto out_unlock;
-	}
+	if (!gdev->chip)
+		return -ENODEV;
 
 	cdev = kzalloc(sizeof(*cdev), GFP_KERNEL);
 	if (!cdev)
-		goto out_unlock;
+		return -ENODEV;
 
 	cdev->watched_lines = bitmap_zalloc(gdev->chip->ngpio, GFP_KERNEL);
 	if (!cdev->watched_lines)
@@ -2830,8 +2743,6 @@  static int gpio_chrdev_open(struct inode *inode, struct file *file)
 	if (ret)
 		goto out_unregister_device_notifier;
 
-	up_read(&gdev->sem);
-
 	return ret;
 
 out_unregister_device_notifier:
@@ -2845,8 +2756,6 @@  static int gpio_chrdev_open(struct inode *inode, struct file *file)
 	bitmap_free(cdev->watched_lines);
 out_free_cdev:
 	kfree(cdev);
-out_unlock:
-	up_read(&gdev->sem);
 	return ret;
 }