ext4: don't read inode block if the buffer has a write error

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
    __ext4_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 __ext4_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>
Cc: sugita <yumiko.sugita.yf@hitachi.com>
Cc: Satoshi OSHIMA <satoshi.oshima.fk@hitachi.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Jan Kara <jack@ucw.cz>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 9843b046c235..efe8caa3811c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3590,6 +3590,16 @@ static int __ext4_get_inode_loc(struct inode *inode,
         }
         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);