[RFC][PATCH] ext3: don't read inode block if the buffer has a write error

Hidehiro Kawai
2008-06-23T11:25:31Z

A transient I/O error can corrupt inode data. Here is the scenario:

(1) update inode_A at the block_B
(2) pdflush writes out new inode_A to the filesystem, but it results
in write I/O error, at this point, BH_Uptodate flag of the buffer
for block_B is cleared and BH_Write_EIO is set
(3) create new inode_C which located at block_B, and
__ext3_get_inode_loc() tries to read on-disk block_B because the
buffer is not uptodate
(4) if it can read on-disk block_B successfully, inode_A is
overwritten by old data

This patch makes __ext3_get_inode_loc() not read the inode block if
the buffer has BH_Write_EIO flag. In this case, the buffer should
have the latest information, so setting the uptodate flag to the
buffer (this avoids WARN_ON_ONCE() in mark_buffer_dirty().)

According to this change, we would need to test BH_Write_EIO flag for
the error checking. Currently nobody checks write I/O errors on
metadata buffers, but it will be done in other patches I'm working on.

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
---
fs/ext3/inode.c | 10 ++++++++++
1 file changed, 10 insertions(+)

Index: linux-2.6.26-rc5-mm3/fs/ext3/inode.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/fs/ext3/inode.c
+++ linux-2.6.26-rc5-mm3/fs/ext3/inode.c
@@ -2516,6 +2516,16 @@ static int __ext3_get_inode_loc(struct i
}
if (!buffer_uptodate(bh)) {
lock_buffer(bh);
+
+ /*
+ * If the buffer has the write error flag, we have failed
+ * to write out another inode in the same block. In this
+ * case, we don't have to read the block because we may
+ * read the old inode data successfully.
+ */
+ if (buffer_write_io_error(bh) && !buffer_uptodate(bh))
+ set_buffer_uptodate(bh);
+
if (buffer_uptodate(bh)) {
/* someone brought it uptodate while we waited */
unlock_buffer(bh);