[PATCH v3 3/3] mm: Wait for writeback when grabbing pages to begin a write

["Darrick J. Wong" <djwong@us.ibm.com>]

When grabbing a page for a buffered IO write, the mm should wait for writeback
on the page to complete so that the page does not become writable during the IO
operation.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
---

 mm/filemap.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index c641edf..c22675f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2287,8 +2287,10 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
 		gfp_notmask = __GFP_FS;
 repeat:
 	page = find_lock_page(mapping, index);
-	if (page)
+	if (page) {
+		wait_on_page_writeback(page);
 		return page;
+	}
 
 	page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~gfp_notmask);
 	if (!page)
@@ -2301,6 +2303,7 @@ repeat:
 			goto repeat;
 		return NULL;
 	}
+	wait_on_page_writeback(page);
 	return page;
 }
 EXPORT_SYMBOL(grab_cache_page_write_begin);