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 914c9a803a05dcfc61559168c9313518eda8bd45..99eee33506ff426ac7507eaabf893965b934a9b9 100644 (file)
--- 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);
 }