[PATCH] spi: Push the BKL down into the drivers

[PATCH] spi: Push the BKL down into the drivers

[Alan Cox]

Another step to removing ->ioctl and to removing the BKL

Signed-off-by: Alan Cox <alan-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index b3518ca..67e907c 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -29,6 +29,7 @@
 #include <linux/errno.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
+#include <linux/smp_lock.h>
 
 #include <linux/spi/spi.h>
 #include <linux/spi/spidev.h>
@@ -240,9 +241,8 @@ done:
 	return status;
 }
 
-static int
-spidev_ioctl(struct inode *inode, struct file *filp,
-		unsigned int cmd, unsigned long arg)
+static long
+spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	int			err = 0;
 	int			retval = 0;
@@ -269,6 +269,7 @@ spidev_ioctl(struct inode *inode, struct file *filp,
 	if (err)
 		return -EFAULT;
 
+	lock_kernel();
 	spidev = filp->private_data;
 	spi = spidev->spi;
 
@@ -357,7 +358,8 @@ spidev_ioctl(struct inode *inode, struct file *filp,
 		/* segmented and/or full-duplex I/O request */
 		if (_IOC_NR(cmd) != _IOC_NR(SPI_IOC_MESSAGE(0))
 				|| _IOC_DIR(cmd) != _IOC_WRITE)
-			return -ENOTTY;
+			retval = -ENOTTY;
+			break;
 
 		tmp = _IOC_SIZE(cmd);
 		if ((tmp % sizeof(struct spi_ioc_transfer)) != 0) {
@@ -385,6 +387,7 @@ spidev_ioctl(struct inode *inode, struct file *filp,
 		kfree(ioc);
 		break;
 	}
+	unlock_kernel();
 	return retval;
 }
 
@@ -447,7 +450,7 @@ static struct file_operations spidev_fops = {
 	 */
 	.write =	spidev_write,
 	.read =		spidev_read,
-	.ioctl =	spidev_ioctl,
+	.unlocked_ioctl = spidev_ioctl,
 	.open =		spidev_open,
 	.release =	spidev_release,
 };

-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/

Re: [PATCH] spi: Push the BKL down into the drivers

[David Brownell]

On Thursday 22 May 2008, Alan Cox wrote:
> Another step to removing ->ioctl and to removing the BKL

This happens to not apply with the latest patches; I'll
address that.

Where is the writeup about exactly what lock_kernel() is
supposed to have been protecting against in ioctl code?

- Dave


-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/

Re: [PATCH] spi: Push the BKL down into the drivers

[Alan Cox]

On Thu, 22 May 2008 17:40:50 -0700
David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org> wrote:

> On Thursday 22 May 2008, Alan Cox wrote:
> > Another step to removing ->ioctl and to removing the BKL
> 
> This happens to not apply with the latest patches; I'll
> address that.
> 
> Where is the writeup about exactly what lock_kernel() is
> supposed to have been protecting against in ioctl code?

There isn't one. The big problem we have is that the ioctl methods were
implicitly called under the big kernel lock. Without pushing them down
into drivers we can't take the step of actually thinking at the driver
level "is this needed". Historically therefore we've never documented
*why* or *if* it was needed - it's just there. Pushing them into the
driver means the subsystem owner gets to see the implicit locking and can
actually ask the right questions with internal driver knowledge.

Whether it is needed is dependant on the internal locking model of the
driver - does it handle parallel ioctls correctly, are there races
against other functions in the driver (eg hot unplugs). That can't be
evaluated at a high level.

It's also made harder by the fact lots of drivers have buggy assumptions
about ioctl locking (watchdog was a fine example).

Alan

-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/