Currently in ext4 direct write path, we update i_disksize only when
new eof is greater than i_size, and don't update it even when new
eof is greater than i_disksize but less than i_size. This doesn't
work well with delalloc buffer write, which updates i_size and
i_disksize only when delalloc blocks are resolved (at writeback
time), the i_disksize from direct write can be lost if a previous
buffer write succeeded at write time but failed at writeback time,
then results in corrupted ondisk inode size.
Consider this case, first buffer write 4k data to a new file at
offset 16k with delayed allocation, then direct write 4k data to the
same file at offset 4k before delalloc blocks are resolved, which
doesn't update i_disksize because it writes within i_size(20k), but
the extent tree metadata has been committed in journal. Then
writeback of the delalloc blocks fails (due to device error etc.),
and i_size/i_disksize from buffer write can't be written to disk
(still zero). A subsequent umount/mount cycle recovers journal and
writes extent tree metadata from direct write to disk, but with
i_disksize being zero.
Fix it by updating i_disksize too in direct write path when new eof
is greater than i_disksize but less than i_size, so i_disksize is
always consistent with direct write.
This fixes occasional i_size corruption in fstests generic/475.
Signed-off-by: Eryu Guan <eguan@xxxxxxxxxx>
---
I think this matches what XFS does in direct write too.
I've tested it by looping generic/475 200 times without hitting a
corruption, usually it fails within 5 iterations for me. Also tested by
full fstests runs on ext2_4k, ext3_2k, ext4_1k configurations and all
results looked good.
fs/ext4/inode.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 534a9130f625..2a75b0aafd31 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3668,7 +3668,7 @@ static ssize_t ext4_direct_IO_write(struct kiocb *iocb, struct iov_iter *iter)
int orphan = 0;
handle_t *handle;
- if (final_size > inode->i_size) {
+ if (final_size > inode->i_size || final_size > ei->i_disksize) {
/* Credits for sb + inode write */
handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
if (IS_ERR(handle)) {
@@ -3780,9 +3780,10 @@ static ssize_t ext4_direct_IO_write(struct kiocb *iocb, struct iov_iter *iter)
ext4_orphan_del(handle, inode);
if (ret > 0) {
loff_t end = offset + ret;
- if (end > inode->i_size) {
+ if (end > inode->i_size || end > ei->i_disksize) {
ei->i_disksize = end;
- i_size_write(inode, end);
+ if (end > inode->i_size)
+ i_size_write(inode, end);
/*
* We're going to return a positive `ret'
* here due to non-zero-length I/O, so there's
--
2.14.3
