From: Frank Mori Hess <fmhess@speakeasy.net>
Date: Fri, 15 Aug 2008 20:42:00 +0000 (+0000)
Subject: The big kernel lock was never held during read() or write() system
X-Git-Url: http://git.tremily.us/?a=commitdiff_plain;h=dbcee2da5cdf11dcd8e8988482f5e269061a5f56;p=comedi.git

The big kernel lock was never held during read() or write() system
calls, only during ioctls.  There should be no reason the device's mutex
needs to be locked during read or write operations.
---

diff --git a/comedi/comedi_fops.c b/comedi/comedi_fops.c
index 914c9a80..99eee335 100644
--- a/comedi/comedi_fops.c
+++ b/comedi/comedi_fops.c
@@ -1496,7 +1496,6 @@ static ssize_t comedi_write(struct file *file, const char *buf, size_t nbytes,
 	const unsigned minor = iminor(file->f_dentry->d_inode);
 
 	dev = comedi_get_device_by_minor(minor);
-	mutex_lock(&dev->mutex);
 	if (!dev->attached) {
 		DPRINTK("no driver configured on comedi%i\n", dev->minor);
 		retval = -ENODEV;
@@ -1558,9 +1557,7 @@ static ssize_t comedi_write(struct file *file, const char *buf, size_t nbytes,
 				retval = -ERESTARTSYS;
 				break;
 			}
-			mutex_unlock(&dev->mutex);
 			schedule();
-			mutex_lock(&dev->mutex);
 			if (!s->busy) {
 				break;
 			}
@@ -1588,8 +1585,7 @@ static ssize_t comedi_write(struct file *file, const char *buf, size_t nbytes,
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&async->wait_head, &wait);
 
-      done:
-	mutex_unlock(&dev->mutex);
+done:
 	return (count ? count : retval);
 }
 
@@ -1603,7 +1599,6 @@ static ssize_t comedi_read(struct file *file, char *buf, size_t nbytes,
 	const unsigned minor = iminor(file->f_dentry->d_inode);
 	comedi_device *dev = comedi_get_device_by_minor(minor);
 
-	mutex_lock(&dev->mutex);
 	if (!dev->attached) {
 		DPRINTK("no driver configured on comedi%i\n", dev->minor);
 		retval = -ENODEV;
@@ -1663,9 +1658,7 @@ static ssize_t comedi_read(struct file *file, char *buf, size_t nbytes,
 				retval = -ERESTARTSYS;
 				break;
 			}
-			mutex_unlock(&dev->mutex);
 			schedule();
-			mutex_lock(&dev->mutex);
 			if (!s->busy) {
 				retval = 0;
 				break;
@@ -1699,8 +1692,7 @@ static ssize_t comedi_read(struct file *file, char *buf, size_t nbytes,
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&async->wait_head, &wait);
 
-      done:
-	mutex_unlock(&dev->mutex);
+done:
 	return (count ? count : retval);
 }