Re: [Kernel BUG] ext4 for v2.6.32 round II

Theodore Tso
2009-10-01T03:02:04Z

Hi Markus,

I'm pretty sure the following should fix your problems; can you
confirm?

- Ted

commit 1f94533d9cd75f6d2826018d54a971b9cc085992
Author: Theodore Ts'o <tytso@mit.edu>
Date: Wed Sep 30 22:57:41 2009 -0400

ext4: fix a BUG_ON crash by checking that page has buffers attached to it

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>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ec367bc..6e65d0e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1146,8 +1146,8 @@ static int check_block_validity(struct inode *inode, const char *msg,
}

/*
- * 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)
@@ -1181,15 +1181,15 @@ static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx,
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;