ext4: BUG_ON fix: check if page has buffers before calling page_buffers()

We need to make check if a page does not have buffes by checking
page_has_buffers(page) before calling page_buffers(page) in
ext4_writepage().  Otherwise page_buffers() could throw a BUG_ON.

Thanks also to Markus Trippelsdorf and Avinash Kurup who also reported
the problem.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reported-by: Sedat Dilek <sedat.dilek@googlemail.com>
Tested-by: Sedat Dilek <sedat.dilek@googlemail.com>

1 files changed, 5 insertions, 7 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 2d6c6c8c036d..191616470466 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2718,7 +2718,7 @@ static int ext4_writepage(struct page *page,
          * try to create them using __block_write_begin.  If this
          * fails, redirty the page and move on.
          */
-        if (!page_buffers(page)) {
+        if (!page_has_buffers(page)) {
                 if (__block_write_begin(page, 0, len,
                                         noalloc_get_block_write)) {
                 redirty_page:
@@ -2732,12 +2732,10 @@ static int ext4_writepage(struct page *page,
         if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                               ext4_bh_delay_or_unwritten)) {
                 /*
-                 * We don't want to do block allocation So redirty the
-                 * page and return We may reach here when we do a
-                 * journal commit via
-                 * journal_submit_inode_data_buffers.  If we don't
-                 * have mapping block we just ignore them. We can also
-                 * reach here via shrink_page_list
+                 * We don't want to do block allocation, so redirty
+                 * the page and return.  We may reach here when we do
+                 * a journal commit via journal_submit_inode_data_buffers.
+                 * We can also reach here via shrink_page_list
                  */
                 goto redirty_page;
         }