[PATCH] btrfs: change the set_page_extent_mapped() call into an ASSERT()

[Qu Wenruo <wqu@suse.com>]

Btrfs uses set_page_extent_mapped() to properly setup a page.

That function would set PagePrivate, and populate needed structure for
subpage.
The timing of calling set_page_extent_mapped() happens before reading a
page or dirtying a page.
Thus when we got a page to write back, if it doesn't have PagePrivate,
it is a big problem in code logic.

Calling set_page_extent_mapped() for such page would just mask the
problem.
Furthermore, for subpage case, we call subpage error helper to clear the
page error bit before calling set_page_extent_mapped().
If we really got a page without Private bit, it can call kernel NULL
pointer dereference.

So change the set_page_extent_mapped() call to an ASSERT(), and move the
check before any page status update call.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 62f0ed2de2b9..219add264acf 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4099,6 +4099,12 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 
 	WARN_ON(!PageLocked(page));
 
+	/*
+	 * All dirty page to be written should have PagePrivate set by
+	 * set_page_extent_mapped() when creating the page.
+	 */
+	ASSERT(PagePrivate(page));
+
 	btrfs_page_clear_error(btrfs_sb(inode->i_sb), page,
 			       page_offset(page), PAGE_SIZE);
 
@@ -4115,12 +4121,6 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 		flush_dcache_page(page);
 	}
 
-	ret = set_page_extent_mapped(page);
-	if (ret < 0) {
-		SetPageError(page);
-		goto done;
-	}
-
 	if (!epd->extent_locked) {
 		ret = writepage_delalloc(BTRFS_I(inode), page, wbc,
 					 &nr_written);
-- 
2.32.0