Re: [PATCH] f2fs: fix fdatasync

From: Chao Yu
Date: Wed Nov 16 2016 - 22:36:33 EST


On 2016/11/17 10:59, Jaegeuk Kim wrote:
> On Thu, Nov 17, 2016 at 10:51:37AM +0800, Chao Yu wrote:
>> Hi Jaegeuk,
>>
>> On 2016/11/17 3:13, Jaegeuk Kim wrote:
>>> Hi Chao,
>>>
>>> On Wed, Nov 16, 2016 at 08:12:11PM +0800, Chao Yu wrote:
>>>> For below two cases, we can't guarantee data consistence:
>>>>
>>>> a)
>>>> 1. xfs_io "pwrite 0 4195328" "fsync"
>>>> 2. xfs_io "pwrite 4195328 1024" "fdatasync"
>>>> 3. godown
>>>> 4. umount & mount
>>>> --> isize we updated before fdatasync won't be recovered
>>>>
>>>> b)
>>>> 1. xfs_io "pwrite -S 0xcc 0 4202496" "fsync"
>>>> 2. xfs_io "fpunch 4194304 4096" "fdatasync"
>>>> 3. godown
>>>> 4. umount & mount
>>>> --> dnode we punched before fdatasync won't be recovered
>>>>
>>>> The reason is that normally fdatasync won't be aware of modification
>>>> of metadata in file, e.g. isize changing, dnode updating, so in ->fsync
>>>> we will skip flushing node pages for above cases, result in making
>>>> fdatasynced file being lost during recovery.
>>>>
>>>> Introduce FDATASYNC_INO global ino cache for tracking node changing,
>>>> later fdatasync choose to flush nodes depend on ino cache state.
>>>
>>> We don't need to add this additionally, and would be better to consider other
>>> major metadata as well.
>>>
>>> How about this?
>>
>> Seems it can't track file after evict?
>
> Do we need that? That means inode page was already up-to-date?

I mean if node/data page of inode were writeback by kworker, after evict, if
user open it again and call fdatasync, after sudden power-off, we will not
recover it.

Thanks,

>
>>
>> Thanks,
>>
>>>
>>> ---
>>> fs/f2fs/f2fs.h | 11 ++++++++++-
>>> fs/f2fs/file.c | 2 +-
>>> 2 files changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index c9672a3..50ffa4f 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -1727,8 +1727,17 @@ static inline void f2fs_i_size_write(struct inode *inode, loff_t i_size)
>>> set_inode_flag(inode, FI_AUTO_RECOVER);
>>> }
>>>
>>> -static inline bool f2fs_skip_inode_update(struct inode *inode)
>>> +static inline bool f2fs_skip_inode_update(struct inode *inode, int dsync)
>>> {
>>> + if (dsync) {
>>> + struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>> + bool ret;
>>> +
>>> + spin_lock(&sbi->inode_lock[DIRTY_META]);
>>> + ret = list_empty(&F2FS_I(inode)->gdirty_list);
>>> + spin_unlock(&sbi->inode_lock[DIRTY_META]);
>>> + return ret;
>>> + }
>>> if (!is_inode_flag_set(inode, FI_AUTO_RECOVER))
>>> return false;
>>> return F2FS_I(inode)->last_disk_size == i_size_read(inode);
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index d48c120..50123c6 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -212,7 +212,7 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>>> }
>>>
>>> /* if the inode is dirty, let's recover all the time */
>>> - if (!datasync && !f2fs_skip_inode_update(inode)) {
>>> + if (!f2fs_skip_inode_update(inode, datasync)) {
>>> f2fs_write_inode(inode, NULL);
>>> goto go_write;
>>> }
>>>
>
> .
>