mm: Wait for writeback when grabbing pages to begin a write

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.  This change is needed to provide page stability during writes for
all filesystems.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 3 insertions, 1 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index bcdc393b6580..dac95a24deac 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2327,7 +2327,7 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
 repeat:
         page = find_lock_page(mapping, index);
         if (page)
-                return page;
+                goto found;
 
         page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~gfp_notmask);
         if (!page)
@@ -2340,6 +2340,8 @@ repeat:
                         goto repeat;
                 return NULL;
         }
+found:
+        wait_on_page_writeback(page);
         return page;
 }
 EXPORT_SYMBOL(grab_cache_page_write_begin);