[RFT PATCH 2/2] fb_defio: redo fix for non-dirty ptes

From: Albert Herranz
Date: Tue May 25 2010 - 18:17:22 EST


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.

LKML-Reference: <20100525160149.GE20853@laptop>
Signed-off-by: Albert Herranz <albert_herranz@xxxxxxxx>
---
drivers/video/fb_defio.c | 12 +++++++++++-
1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
index 0e4dcdb..a3e8cc7 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 = {
--
1.7.0.4

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