[50/90] ext4: fix a BUG_ON crash by checking that page has buffers attached to it

Greg KH
2009-12-11T04:50:03Z

[-- Attachment #1: 0050-ext4-fix-a-BUG_ON-crash-by-checking-that-page-has-bu.patch --]
[-- Type: text/plain, Size: 1630 bytes --]

2.6.31-stable review patch. If anyone has any objections, please let us know.

------------------
(cherry picked from commit 1f94533d9cd75f6d2826018d54a971b9cc085992)

In ext4_num_dirty_pages() we were calling page_buffers() before
checking to see if the page actually had pages attached to it; this
would cause a BUG check crash in the inline function page_buffers().

Thanks to Markus Trippelsdorf for reporting this bug.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/ext4/inode.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1147,8 +1147,8 @@ static int check_block_validity(struct i
}

/*
- * Return the number of dirty pages in the given inode starting at
- * page frame idx.
+ * Return the number of contiguous dirty pages in a given inode
+ * starting at page frame idx.
*/
static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx,
unsigned int max_pages)
@@ -1182,15 +1182,15 @@ static pgoff_t ext4_num_dirty_pages(stru
unlock_page(page);
break;
}
- head = page_buffers(page);
- bh = head;
- do {
- if (!buffer_delay(bh) &&
- !buffer_unwritten(bh)) {
- done = 1;
- break;
- }
- } while ((bh = bh->b_this_page) != head);
+ if (page_has_buffers(page)) {
+ bh = head = page_buffers(page);
+ do {
+ if (!buffer_delay(bh) &&
+ !buffer_unwritten(bh))
+ done = 1;
+ bh = bh->b_this_page;
+ } while (!done && (bh != head));
+ }
unlock_page(page);
if (done)
break;