fb_defio: redo fix for non-dirty ptes

As pointed by Nick Piggin, ->page_mkwrite provides a way to keep a page
locked until the associated PTE is marked dirty.

Re-implement the fix by using this mechanism.

Signed-off-by: Albert Herranz <albert_herranz@yahoo.es>
Acked-by: Jaya Kumar <jayakumar.lkml@gmail.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 1 deletions

diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
index 137100ea8ad7..6b93ef93cb12 100644
--- a/drivers/video/fb_defio.c
+++ b/drivers/video/fb_defio.c
@@ -100,6 +100,16 @@ static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
         /* protect against the workqueue changing the page list */
         mutex_lock(&fbdefio->lock);
 
+        /*
+         * We want the page to remain locked from ->page_mkwrite until
+         * the PTE is marked dirty to avoid page_mkclean() being called
+         * before the PTE is updated, which would leave the page ignored
+         * by defio.
+         * Do this by locking the page here and informing the caller
+         * about it with VM_FAULT_LOCKED.
+         */
+        lock_page(page);
+
         /* we loop through the pagelist before adding in order
         to keep the pagelist sorted */
         list_for_each_entry(cur, &fbdefio->pagelist, lru) {
@@ -121,7 +131,7 @@ page_already_added:
 
         /* come back after delay to process the deferred IO */
         schedule_delayed_work(&info->deferred_work, fbdefio->delay);
-        return 0;
+        return VM_FAULT_LOCKED;
 }
 
 static const struct vm_operations_struct fb_deferred_io_vm_ops = {