Jan Kara <jack@xxxxxxx> writes: > Gao Xiang has reported that on ext4 O_SYNC direct IO does not properly > sync file size update and thus if we crash at unfortunate moment, the > file can have smaller size although O_SYNC IO has reported successful > completion. The problem happens because update of on-disk inode size is > handled in ext4_dio_write_iter() *after* iomap_dio_rw() (and thus > dio_complete() in particular) has returned and generic_file_sync() gets > called by dio_complete(). Fix the problem by handling on-disk inode size > update directly in our ->end_io completion handler. > > References: https://lore.kernel.org/all/02d18236-26ef-09b0-90ad-030c4fe3ee20@xxxxxxxxxxxxxxxxx > Reported-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> Guess we need a fixes tag. > --- > fs/ext4/file.c | 139 ++++++++++++++++++------------------------------- > 1 file changed, 52 insertions(+), 87 deletions(-) > > So finally I've hopefully got all the corner cases right ;) At least fstest > pass now. > > diff --git a/fs/ext4/file.c b/fs/ext4/file.c > index 1492b1ae21f4..d0711c1a9b06 100644 > --- a/fs/ext4/file.c > +++ b/fs/ext4/file.c > @@ -306,80 +306,34 @@ static ssize_t ext4_buffered_write_iter(struct kiocb *iocb, > } > > static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset, > - ssize_t written, size_t count) > + ssize_t count) > { > handle_t *handle; > - bool truncate = false; > - u8 blkbits = inode->i_blkbits; > - ext4_lblk_t written_blk, end_blk; > - int ret; > - > - /* > - * Note that EXT4_I(inode)->i_disksize can get extended up to > - * inode->i_size while the I/O was running due to writeback of delalloc > - * blocks. But, the code in ext4_iomap_alloc() is careful to use > - * zeroed/unwritten extents if this is possible; thus we won't leave > - * uninitialized blocks in a file even if we didn't succeed in writing > - * as much as we intended. > - */ > - WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize); > - if (offset + count <= EXT4_I(inode)->i_disksize) { > - /* > - * We need to ensure that the inode is removed from the orphan > - * list if it has been added prematurely, due to writeback of > - * delalloc blocks. > - */ > - if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) { > - handle = ext4_journal_start(inode, EXT4_HT_INODE, 2); > - > - if (IS_ERR(handle)) { > - ext4_orphan_del(NULL, inode); > - return PTR_ERR(handle); > - } > - > - ext4_orphan_del(handle, inode); > - ext4_journal_stop(handle); > - } > - > - return written; > - } > - > - if (written < 0) > - goto truncate; > > + lockdep_assert_held_write(&inode->i_rwsem); > handle = ext4_journal_start(inode, EXT4_HT_INODE, 2); > - if (IS_ERR(handle)) { > - written = PTR_ERR(handle); > - goto truncate; > - } > + if (IS_ERR(handle)) > + return PTR_ERR(handle); > > - if (ext4_update_inode_size(inode, offset + written)) { > - ret = ext4_mark_inode_dirty(handle, inode); > + if (ext4_update_inode_size(inode, offset + count)) { > + int ret = ext4_mark_inode_dirty(handle, inode); > if (unlikely(ret)) { > - written = ret; > ext4_journal_stop(handle); > - goto truncate; > + return ret; > } > } > > - /* > - * We may need to truncate allocated but not written blocks beyond EOF. > - */ > - written_blk = ALIGN(offset + written, 1 << blkbits); > - end_blk = ALIGN(offset + count, 1 << blkbits); > - if (written_blk < end_blk && ext4_can_truncate(inode)) > - truncate = true; > - > - /* > - * Remove the inode from the orphan list if it has been extended and > - * everything went OK. > - */ > - if (!truncate && inode->i_nlink) > + if (inode->i_nlink) > ext4_orphan_del(handle, inode); > ext4_journal_stop(handle); > > - if (truncate) { > -truncate: > + return count; > +} > + > +static void ext4_inode_extension_cleanup(struct inode *inode, ssize_t count) > +{ > + lockdep_assert_held_write(&inode->i_rwsem); > + if (count < 0) { > ext4_truncate_failed_write(inode); > /* > * If the truncate operation failed early, then the inode may > @@ -388,9 +342,28 @@ static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset, > */ > if (inode->i_nlink) > ext4_orphan_del(NULL, inode); > + return; > } > + /* > + * If i_disksize got extended due to writeback of delalloc blocks while > + * the DIO was running we could fail to cleanup the orphan list in > + * ext4_handle_inode_extension(). Do it now. > + */ > + if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) { > + handle_t *handle = ext4_journal_start(inode, EXT4_HT_INODE, 2); > > - return written; > + if (IS_ERR(handle)) { > + /* > + * The write has successfully completed. Not much to > + * do with the error here so just cleanup the orphan > + * list and hope for the best. > + */ > + ext4_orphan_del(NULL, inode); > + return; > + } > + ext4_orphan_del(handle, inode); > + ext4_journal_stop(handle); > + } > } > > static int ext4_dio_write_end_io(struct kiocb *iocb, ssize_t size, > @@ -399,31 +372,22 @@ static int ext4_dio_write_end_io(struct kiocb *iocb, ssize_t size, > loff_t pos = iocb->ki_pos; > struct inode *inode = file_inode(iocb->ki_filp); > > + if (!error && size && flags & IOMAP_DIO_END_UNWRITTEN) Do we have IOMAP_DIO_END_UNWRITTEN? or should it be IOMAP_DIO_UNWRITTEN? Also we don't need to check !error case if we return early in case of an error. > + error = ext4_convert_unwritten_extents(NULL, inode, pos, size); > if (error) > return error; > - > - if (size && flags & IOMAP_DIO_END_UNWRITTEN) { ditto. > - error = ext4_convert_unwritten_extents(NULL, inode, pos, size); > - if (error < 0) > - return error; > - } > /* > - * If we are extending the file, we have to update i_size here before > - * page cache gets invalidated in iomap_dio_rw(). Otherwise racing > - * buffered reads could zero out too much from page cache pages. Update > - * of on-disk size will happen later in ext4_dio_write_iter() where > - * we have enough information to also perform orphan list handling etc. > - * Note that we perform all extending writes synchronously under > - * i_rwsem held exclusively so i_size update is safe here in that case. > - * If the write was not extending, we cannot see pos > i_size here > - * because operations reducing i_size like truncate wait for all > - * outstanding DIO before updating i_size. > + * Note that EXT4_I(inode)->i_disksize can get extended up to > + * inode->i_size while the I/O was running due to writeback of delalloc > + * blocks. But the code in ext4_iomap_alloc() is careful to use > + * zeroed/unwritten extents if this is possible; thus we won't leave > + * uninitialized blocks in a file even if we didn't succeed in writing > + * as much as we intended. > */ > - pos += size; > - if (pos > i_size_read(inode)) > - i_size_write(inode, pos); > - > - return 0; > + WARN_ON_ONCE(i_size_read(inode) < READ_ONCE(EXT4_I(inode)->i_disksize)); > + if (pos + size <= READ_ONCE(EXT4_I(inode)->i_disksize)) > + return 0; > + return ext4_handle_inode_extension(inode, pos, size); > } Although it is not a problem, but we are sometimes returning 0 and sometimes count here. > > static const struct iomap_dio_ops ext4_dio_write_ops = { > @@ -606,9 +570,8 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from) > dio_flags, NULL, 0); > if (ret == -ENOTBLK) > ret = 0; > - > if (extend) > - ret = ext4_handle_inode_extension(inode, offset, ret, count); > + ext4_inode_extension_cleanup(inode, ret); > > out: > if (ilock_shared) > @@ -689,8 +652,10 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from) > > ret = dax_iomap_rw(iocb, from, &ext4_iomap_ops); > > - if (extend) > - ret = ext4_handle_inode_extension(inode, offset, ret, count); > + if (extend) { > + ret = ext4_handle_inode_extension(inode, offset, ret); > + ext4_inode_extension_cleanup(inode, ret); ok, looks like we are using that return value here. > + } > out: > inode_unlock(inode); > if (ret > 0) > -- > 2.35.3 Otherwise it looks good to me. -ritesh
