fbdev: bugfix for multiprocess defio

[uclinux-h8/linux.git] / drivers / video / fb_defio.c

diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
index 24843fd..59df132 100644 (file)
--- a/drivers/video/fb_defio.c
+++ b/drivers/video/fb_defio.c
@@ -74,6 +74,7 @@ static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
 {
        struct fb_info *info = vma->vm_private_data;
        struct fb_deferred_io *fbdefio = info->fbdefio;
+       struct page *cur;
 
        /* this is a callback we get when userspace first tries to
        write to the page. we schedule a workqueue. that workqueue
@@ -83,7 +84,24 @@ static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
 
        /* protect against the workqueue changing the page list */
        mutex_lock(&fbdefio->lock);
-       list_add(&page->lru, &fbdefio->pagelist);
+
+       /* we loop through the pagelist before adding in order
+       to keep the pagelist sorted */
+       list_for_each_entry(cur, &fbdefio->pagelist, lru) {
+               /* this check is to catch the case where a new
+               process could start writing to the same page
+               through a new pte. this new access can cause the
+               mkwrite even when the original ps's pte is marked
+               writable */
+               if (unlikely(cur == page))
+                       goto page_already_added;
+               else if (cur->index > page->index)
+                       break;
+       }
+
+       list_add_tail(&page->lru, &cur->lru);
+
+page_already_added:
        mutex_unlock(&fbdefio->lock);
 
        /* come back after delay to process the deferred IO */