Merge 3.15-rc2 into staging-next

This resolves a bunch of merge errors with other fixes that are already
in Linus's tree.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 14 insertions, 4 deletions

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index e283e6c..70545e6 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1925,14 +1925,21 @@ static int comedi_mmap(struct file *file, struct vm_area_struct *vma)
 	struct comedi_device *dev = file->private_data;
 	struct comedi_subdevice *s;
 	struct comedi_async *async;
-	struct comedi_buf_map *bm;
+	struct comedi_buf_map *bm = NULL;
 	unsigned long start = vma->vm_start;
 	unsigned long size;
 	int n_pages;
 	int i;
 	int retval;
 
-	mutex_lock(&dev->mutex);
+	/*
+	 * 'trylock' avoids circular dependency with current->mm->mmap_sem
+	 * and down-reading &dev->attach_lock should normally succeed without
+	 * contention unless the device is in the process of being attached
+	 * or detached.
+	 */
+	if (!down_read_trylock(&dev->attach_lock))
+		return -EAGAIN;
 
 	if (!dev->attached) {
 		dev_dbg(dev->class_dev, "no driver attached\n");
@@ -1972,7 +1979,9 @@ static int comedi_mmap(struct file *file, struct vm_area_struct *vma)
 	}
 
 	n_pages = size >> PAGE_SHIFT;
-	bm = async->buf_map;
+
+	/* get reference to current buf map (if any) */
+	bm = comedi_buf_map_from_subdev_get(s);
 	if (!bm || n_pages > bm->n_pages) {
 		retval = -EINVAL;
 		goto done;
@@ -1996,7 +2005,8 @@ static int comedi_mmap(struct file *file, struct vm_area_struct *vma)
 
 	retval = 0;
 done:
-	mutex_unlock(&dev->mutex);
+	up_read(&dev->attach_lock);
+	comedi_buf_map_put(bm);	/* put reference to buf map - okay if NULL */
 	return retval;
 }