linux-ext4 - [PATCH 11/12] ext4: Make ext4_bio_writepage() handle unprepared buffers

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Date:	Fri, 18 Jan 2013 13:00:45 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ted Tso <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: [PATCH 11/12] ext4: Make ext4_bio_writepage() handle unprepared buffers

So far ext4_bio_writepage() unconditionally cleared dirty bit on all buffers
underlying the page. That implicitely assumes we can write all buffers. So
far that is true because callers call into ext4_bio_writepage() make sure
all buffers in the page are mapped but
a) it's a data corruption bug waiting to happen
b) in data=ordered mode when blocksize < pagesize we do need to write pages
   that may have only some of dirty buffers mapped.

So change ext4_bio_writepage() to skip buffers that cannot be written without
clearing their dirty bit.

Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/page-io.c |   17 +++++++++--------
 1 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 3fb385c..0290bf8 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -350,14 +350,6 @@ static int io_submit_add_bh(struct ext4_io_submit *io,
 		unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
 	}
 
-	if (!buffer_mapped(bh) || buffer_delay(bh)) {
-		if (!buffer_mapped(bh))
-			clear_buffer_dirty(bh);
-		if (io->io_bio)
-			ext4_io_submit(io);
-		return 0;
-	}
-
 	if (io->io_bio && bh->b_blocknr != io->io_next_block) {
 submit_and_retry:
 		ext4_io_submit(io);
@@ -436,6 +428,15 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 			set_buffer_uptodate(bh);
 			continue;
 		}
+		if (!buffer_dirty(bh) || buffer_delay(bh) ||
+		    !buffer_mapped(bh) || buffer_unwritten(bh)) {
+			/* A hole? We can safely clear the dirty bit */
+			if (!buffer_mapped(bh))
+				clear_buffer_dirty(bh);
+			if (io->io_bio)
+				ext4_io_submit(io);
+			continue;
+		}
 		ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
 		if (ret) {
 			/*
-- 
1.7.1

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