2011-04-22 17:52:18

by Curt Wohlgemuth

Subject: [PATCH] ext4: Don't set PageUptodate in ext4_end_bio()

In the bio completion routine, we should not be setting
PageUptodate at all -- it's set at sys_write() time, and is
unaffected by success/failure of the write to disk.

This can cause a page corruption bug when

block size < page size

if we have only written a single block -- we might end up
setting the entire PageUptodate, which will cause subsequent
reads to get bad data.

Signed-off-by: Curt Wohlgemuth <[email protected]>
Reported-by: Jim Meyering <[email protected]>
Reported-by: Hugh Dickins <[email protected]>
Cc: Mingming Cao <[email protected]>
---
fs/ext4/page-io.c | 41 +++++------------------------------------
1 files changed, 5 insertions(+), 36 deletions(-)

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index b6dbd05..76bbe6a 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -202,47 +202,16 @@ static void ext4_end_bio(struct bio *bio, int error)

for (i = 0; i < io_end->num_io_pages; i++) {
struct page *page = io_end->pages[i]->p_page;
- struct buffer_head *bh, *head;
- int partial_write = 0;
+ struct buffer_head *head;

head = page_buffers(page);
- if (error)
- SetPageError(page);
BUG_ON(!head);
- if (head->b_size != PAGE_CACHE_SIZE) {
- loff_t offset;
- loff_t io_end_offset = io_end->offset + io_end->size;
-
- offset = (sector_t) page->index << PAGE_CACHE_SHIFT;
- bh = head;
- do {
- if ((offset >= io_end->offset) &&
- (offset+bh->b_size <= io_end_offset)) {
- if (error)
- buffer_io_error(bh);
-
- }
- if (buffer_delay(bh))
- partial_write = 1;
- else if (!buffer_mapped(bh))
- clear_buffer_dirty(bh);
- else if (buffer_dirty(bh))
- partial_write = 1;
- offset += bh->b_size;
- bh = bh->b_this_page;
- } while (bh != head);
+ if (error) {
+ SetPageError(page);
+ buffer_io_error(head);
+ set_bit(AS_EIO, &page->mapping->flags);
}

- /*
- * If this is a partial write which happened to make
- * all buffers uptodate then we can optimize away a
- * bogus readpage() for the next read(). Here we
- * 'discover' whether the page went uptodate as a
- * result of this (potentially partial) write.
- */
- if (!partial_write)
- SetPageUptodate(page);

2011-05-01 21:56:46

by Theodore Ts'o

Subject: Re: [PATCH] ext4: Don't set PageUptodate in ext4_end_bio()

On Fri, Apr 22, 2011 at 10:51:58AM -0700, Curt Wohlgemuth wrote:
> In the bio completion routine, we should not be setting
> PageUptodate at all -- it's set at sys_write() time, and is
> unaffected by success/failure of the write to disk.
>
> This can cause a page corruption bug when
>
> block size < page size
>
> if we have only written a single block -- we might end up
> setting the entire PageUptodate, which will cause subsequent
> reads to get bad data.
>
> Signed-off-by: Curt Wohlgemuth <[email protected]>
> Reported-by: Jim Meyering <[email protected]>
> Reported-by: Hugh Dickins <[email protected]>
> Cc: Mingming Cao <[email protected]>

Thanks, I've added this to the ext4 tree.

- Ted