On Fri 17-03-23 09:35:53, Zhihao Cheng wrote:
> Following process makes i_disksize exceed i_size:
>
> generic_perform_write
> copied = iov_iter_copy_from_user_atomic(len) // copied < len
> ext4_da_write_end
> | ext4_update_i_disksize
> | new_i_size = pos + copied;
> | WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
> | generic_write_end
> | copied = block_write_end(copied, len) // copied = 0
> | if (unlikely(copied < len))
> | if (!PageUptodate(page))
> | copied = 0;
> | if (pos + copied > inode->i_size) // return false
> if (unlikely(copied == 0))
> goto again;
> if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
> status = -EFAULT;
> break;
> }
>
> We get i_disksize greater than i_size here, which could trigger WARNING
> check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:
>
> ext4_dio_write_iter
> iomap_dio_rw
> __iomap_dio_rw // return err, length is not aligned to 512
> ext4_handle_inode_extension
> WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops
>
> WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
> CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
> RIP: 0010:ext4_file_write_iter+0xbc7
> Call Trace:
> vfs_write+0x3b1
> ksys_write+0x77
> do_syscall_64+0x39
>
> Fix it by putting block_write_end() before i_disksize updating just
> like ext4_write_end() does.
>
> Fetch a reproducer in [Link].
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
> Fixes: 64769240bd07f ("ext4: Add delayed allocation support in data=writeback mode")
> Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
Good catch (although practically this will hardly have any negative
effect). But rather than opencoding generic_write_end() I'd do:
if (unlikely(copied < len) && !PageUptodate(page))
copied = 0;
at the beginning of ext4_da_write_end() and that should solve these
problems as well?
Honza
> ---
> fs/ext4/inode.c | 32 +++++++++++++++++++++++++-------
> 1 file changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index bf0b7dea4900..577dc23f3b78 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3136,6 +3136,8 @@ static int ext4_da_write_end(struct file *file,
> loff_t new_i_size;
> unsigned long start, end;
> int write_mode = (int)(unsigned long)fsdata;
> + bool i_size_changed = false;
> + loff_t old_size = inode->i_size;
>
> if (write_mode == FALL_BACK_TO_NONDELALLOC)
> return ext4_write_end(file, mapping, pos,
> @@ -3148,6 +3150,8 @@ static int ext4_da_write_end(struct file *file,
> ext4_has_inline_data(inode))
> return ext4_write_inline_data_end(inode, pos, len, copied, page);
>
> + copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
> +
> start = pos & (PAGE_SIZE - 1);
> end = start + copied - 1;
>
> @@ -3162,16 +3166,30 @@ static int ext4_da_write_end(struct file *file,
> * check), we need to update i_disksize here as neither
> * ext4_writepage() nor certain ext4_writepages() paths not
> * allocating blocks update i_disksize.
> - *
> - * Note that we defer inode dirtying to generic_write_end() /
> - * ext4_da_write_inline_data_end().
> */
> new_i_size = pos + copied;
> - if (copied && new_i_size > inode->i_size &&
> - ext4_da_should_update_i_disksize(page, end))
> - ext4_update_i_disksize(inode, new_i_size);
> + if (new_i_size > inode->i_size) {
> + i_size_write(inode, new_i_size);
> + i_size_changed = true;
> + if (copied && ext4_da_should_update_i_disksize(page, end))
> + ext4_update_i_disksize(inode, new_i_size);
> + }
> +
> + unlock_page(page);
> + put_page(page);
> +
> + if (old_size < pos)
> + pagecache_isize_extended(inode, old_size, pos);
> + /*
> + * Don't mark the inode dirty under page lock. First, it unnecessarily
> + * makes the holding time of page lock longer. Second, it forces lock
> + * ordering of page lock and transaction start for journaling
> + * filesystems.
> + */
> + if (i_size_changed)
> + mark_inode_dirty(inode);
>
> - return generic_write_end(file, mapping, pos, len, copied, page, fsdata);
> + return copied;
> }
>
> /*
> --
> 2.31.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
