linux-ext4 - [PATCH 2/2] ext4: Fix buffer dirtying in data=journal mode

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Date:	Mon, 21 Jun 2010 12:42:53 +0200
From:	Jan Kara <jack@...e.cz>
To:	linux-ext4@...r.kernel.org
Cc:	Jan Kara <jack@...e.cz>, tytso@....edu
Subject: [PATCH 2/2] ext4: Fix buffer dirtying in data=journal mode

block_prepare_write() can dirty freshly created buffer. This is a problem
for data=journal mode because data buffers shouldn't be dirty unless they
are undergoing checkpoint. So we have to tweak get_block function for
data=journal mode to catch the case when block_prepare_write would dirty
the buffer, do the work instead of block_prepare_write, and properly handle
dirty buffer as data=journal mode requires it.

It might be cleaner to avoid using block_prepare_write() for data=journal
mode writes but that would require us to duplicate most of the function
which isn't nice either...

CC: tytso@....edu
Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/inode.c |   47 +++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 81d6054..526404b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1388,6 +1388,43 @@ out:
 	return ret;
 }
 
+static int ext4_journalled_get_block(struct inode *inode, sector_t iblock,
+				     struct buffer_head *bh, int create)
+{
+	handle_t *handle = ext4_journal_current_handle();
+	int ret;
+
+	/* This function should ever be used only for real buffers */
+	BUG_ON(!bh->b_page);
+
+	ret = ext4_get_blocks(handle, inode, iblock, 1, bh,
+			      create ? EXT4_GET_BLOCKS_CREATE : 0);
+	if (ret > 0) {
+		if (buffer_new(bh)) {
+			struct page *page = bh->b_page;
+
+			/*
+			 * This is a terrible hack to avoid block_prepare_write
+			 * marking our buffer as dirty
+			 */
+			if (PageUptodate(page)) {
+				ret = ext4_journal_get_write_access(handle, bh);
+				if (ret < 0)
+					return ret;
+				unmap_underlying_metadata(bh->b_bdev,
+							  bh->b_blocknr);
+				clear_buffer_new(bh);
+				set_buffer_uptodate(bh);
+				ret = jbd2_journal_dirty_metadata(handle, bh);
+				if (ret < 0)
+					return ret;
+			}
+		}
+		ret = 0;
+	}
+	return ret;
+}
+
 /*
  * `handle' can be NULL if create is zero
  */
@@ -1599,12 +1636,14 @@ retry:
 	if (ext4_should_dioread_nolock(inode))
 		ret = block_write_begin(file, mapping, pos, len, flags, pagep,
 				fsdata, ext4_get_block_write);
-	else
+	else if (!ext4_should_journal_data(inode))
 		ret = block_write_begin(file, mapping, pos, len, flags, pagep,
 				fsdata, ext4_get_block);
-
-	if (!ret && ext4_should_journal_data(inode)) {
-		ret = walk_page_buffers(handle, page_buffers(page),
+	else {
+		ret = block_write_begin(file, mapping, pos, len, flags, pagep,
+				fsdata, ext4_journalled_get_block);
+		if (!ret)
+			ret = walk_page_buffers(handle, page_buffers(page),
 				from, to, NULL, do_journal_get_write_access);
 	}
 
-- 
1.6.4.2

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