spi: Push the BKL down into the drivers

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

index b3518ca..67e907c 100644
@@ -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,
 };

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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

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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

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