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Message-ID: <c37e682d-a5b3-c23d-0a2c-e09474b64426@huawei.com> Date: Thu, 4 Apr 2019 20:46:47 +0800 From: "zhangyi (F)" <yi.zhang@...wei.com> To: Jan Kara <jack@...e.cz> CC: <linux-ext4@...r.kernel.org>, <tytso@....edu>, <adilger.kernel@...ger.ca>, <miaoxie@...wei.com> Subject: Re: [PATCH] ext4: add inode to ordered data list when extending file without block allocation On 2019/4/4 18:18, Jan Kara Wrote: > On Thu 04-04-19 17:29:52, zhangyi (F) wrote: >> Currently we capture a NULL data exposure problem after a crash or >> poweroff when append writing a file in the data=ordered mode. The >> problem is that we were not add inode to the transaction's order data >> list when updating i_disksize without new block allocation no matter >> the delay allocated block feature is enabled or not. >> >> write jbd2 writeback >> append write in allocated block >> mark buffer dirty >> update i_disksize >> mark inode dirty >> commit transaction >> write inode >> (data exposure after a crash) >> write dirty buffer >> >> It's fine in the case of new block allocation because we do this job in >> ext4_map_blocks(). To fix this problem, this patch add inode to current >> transaction's order data list after new data is copied and needing >> update i_disksize in the case of no block allocation. >> >> Fixes: 06bd3c36a733ac ("ext4: fix data exposure after a crash") >> Fixes: f3b59291a69d0b ("ext4: remove calls to ext4_jbd2_file_inode() from delalloc write path") >> Signed-off-by: zhangyi (F) <yi.zhang@...wei.com> > > Thanks for the patch. The current behavior is a deliberate decision. > data=ordered mode does guarantee there is no stale data visible in case of > crash. However it does not guarantee you cannot see zeros where data was > written. > Hi Jan, Thanks a lot for your explanation. I read the Documentation/admin-guide/ext4.rst, which said about the ordered mode: > ... When it's time to write the new metadata out to disk, the associated data > blocks are written first... So I reckon that the dirty data block should be written to disk before committing i_disksize and we cannot see the zero data. Now, I don't find any offical docs to record the behavior you mentioned, do you have some links talk about this behavior or am I miss something ? Thanks, Yi. >> --- >> fs/ext4/inode.c | 19 +++++++++++++++++++ >> 1 file changed, 19 insertions(+) >> >> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c >> index b32a57b..5cfa066 100644 >> --- a/fs/ext4/inode.c >> +++ b/fs/ext4/inode.c >> @@ -1419,6 +1419,16 @@ static int ext4_write_end(struct file *file, >> if (i_size_changed || inline_data) >> ext4_mark_inode_dirty(handle, inode); >> >> + /* >> + * Updating i_disksize when extending file without block >> + * allocation, the newly written data where should be visible >> + * after transaction commit must be on transaction's ordered >> + * data list. >> + */ >> + if (copied && (i_size_changed & 0x2) && >> + ext4_should_order_data(inode)) >> + ext4_jbd2_inode_add_write(handle, inode); >> + >> if (pos + len > inode->i_size && ext4_can_truncate(inode)) >> /* if we have allocated more blocks and copied >> * less. We will have blocks allocated outside >> @@ -3185,6 +3195,15 @@ static int ext4_da_write_end(struct file *file, >> * bu greater than i_disksize.(hint delalloc) >> */ >> ext4_mark_inode_dirty(handle, inode); >> + >> + /* >> + * Updating i_disksize when extending file without >> + * block allocation, the newly written data where >> + * should be visible after transaction commit must >> + * be on transaction's ordered data list. >> + */ >> + if (ext4_should_order_data(inode)) >> + ext4_jbd2_inode_add_write(handle, inode); >> } >> } >> >> -- >> 2.7.4 >>
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