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

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

[Curt Wohlgemuth]

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.

This commit also fixes ext4_end_bio() to set AS_EIO in the
page->mapping->flags on error, which was left out by
mistake.

Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Reported-by: Jim Meyering <jim@meyering.net>
Reported-by: Hugh Dickins <hughd@google.com>
Cc: Mingming Cao <cmm@us.ibm.com>
---
Changlog since v1:
- Added commit message text about setting AS_EIO for the
  page on error.
- Continue to loop over all BHs in a page and emit unique
  errors for each of them.
---
 fs/ext4/page-io.c |   22 ++++------------------
 1 files changed, 4 insertions(+), 18 deletions(-)

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index b6dbd05..fb681cf 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -203,11 +203,12 @@ 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;
 
 		head = page_buffers(page);
-		if (error)
+		if (error) {
 			SetPageError(page);
+			set_bit(AS_EIO, &page->mapping->flags);
+		}
 		BUG_ON(!head);
 		if (head->b_size != PAGE_CACHE_SIZE) {
 			loff_t offset;
@@ -220,29 +221,14 @@ static void ext4_end_bio(struct bio *bio, int error)
 				    (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))
+				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 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);

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

[Curt Wohlgemuth]

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 <curtw@google.com>
Reported-by: Jim Meyering <jim@meyering.net>
Reported-by: Hugh Dickins <hughd@google.com>
Cc: Mingming Cao <cmm@us.ibm.com>
---
 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);

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

[Ted Ts'o]

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 <curtw@google.com>
> Reported-by: Jim Meyering <jim@meyering.net>
> Reported-by: Hugh Dickins <hughd@google.com>
> Cc: Mingming Cao <cmm@us.ibm.com>

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

					- Ted