Re: [PATCH v3 0/3] data integrity: Stabilize pages during writeback for ext4

["Darrick J. Wong" <djwong@us.ibm.com>]

On Wed, May 04, 2011 at 03:21:55PM -0400, Chris Mason wrote:
> Excerpts from Christoph Hellwig's message of 2011-05-04 14:46:44 -0400:
> > This seems to miss out on a lot of the generic functionality like
> > write_cache_pages and block_page_mkwrite and just patch it into
> > the ext4 copy & paste variants.  Please make sure your patches also
> > work for filesystem that use more of the generic functionality like
> > xfs or ext2 (the latter one might be fun for the mmap case).
> 
> Probably after the block_commit_write in block_page_mkwrite()
> Another question is, do we want to introduce a wait_on_stable_page_writeback()?

Something like this here?  It fixes block_page_mkwrite users and sticks in a
simple page_mkwrite for fses that don't provide one at all.  From a quick wac
run it seems to make xfs work.  ext2 seems to have some issues with modifying a
buffer_head's bh_data without locking the bh during the update, so I guess it
needs some review.

--D

--

fs: Modify/provide generic writepage/page_mkwrite functions to wait for writeback

Modify the generic writepage function, and add an empty page_mkwrite function,
to wait for page writeback to finish before allowing writes.  This is so that
simple filesystems have stable pages during write operations.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
---

 fs/buffer.c  |    1 +
 mm/filemap.c |   10 ++++++++++
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index a08bb8e..cf9a795 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2361,6 +2361,7 @@ block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 	if (!ret)
 		ret = block_commit_write(page, 0, end);
 
+	wait_on_page_writeback(page);
 	if (unlikely(ret)) {
 		unlock_page(page);
 		if (ret == -ENOMEM)
diff --git a/mm/filemap.c b/mm/filemap.c
index c22675f..9cb4e51 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1713,8 +1713,18 @@ page_not_uptodate:
 }
 EXPORT_SYMBOL(filemap_fault);
 
+static int empty_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+	struct page *page = vmf->page;
+
+	lock_page(page);
+	wait_on_page_writeback(page);
+	return VM_FAULT_LOCKED;
+}
+
 const struct vm_operations_struct generic_file_vm_ops = {
 	.fault		= filemap_fault,
+	.page_mkwrite	= empty_page_mkwrite,
 };
 
 /* This is used for a general mmap of a disk file */
--

Here's the beginning of a patch against ext2 also.  It fixes most of the
checksum errors when metadata writes are in progress, though I suspect there
are more spots that I haven't caught yet.

--

ext2: Lock buffer_heads during metadata update

ext2 does not protect buffer head that represent metadata against modifications
during write operations.  This is a problem if the memory buffer needs to be
stable during writes; I think there are a few more spots in ext2 that need this
treatment. :)

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
---

 fs/ext2/inode.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 788e09a..5314b0b 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -1426,6 +1426,7 @@ static int __ext2_write_inode(struct inode *inode, int do_sync)
 	if (IS_ERR(raw_inode))
  		return -EIO;
 
+	lock_buffer(bh);
 	/* For fields not not tracking in the in-memory inode,
 	 * initialise them to zero for new inodes. */
 	if (ei->i_state & EXT2_STATE_NEW)
@@ -1502,6 +1503,8 @@ static int __ext2_write_inode(struct inode *inode, int do_sync)
 		}
 	} else for (n = 0; n < EXT2_N_BLOCKS; n++)
 		raw_inode->i_block[n] = ei->i_data[n];
+	unlock_buffer(bh);
+
 	mark_buffer_dirty(bh);
 	if (do_sync) {
 		sync_dirty_buffer(bh);

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