linux-kernel - Re: [PATCH] f2fs: add fi->commit_lock to protect commit GCed pages

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Date:   Fri, 9 Feb 2018 20:56:56 +0800
From:   Yunlong Song <yunlong.song@...wei.com>
To:     Chao Yu <chao@...nel.org>, <jaegeuk@...nel.org>,
        <yuchao0@...wei.com>, <yunlong.song@...oud.com>
CC:     <miaoxie@...wei.com>, <bintian.wang@...wei.com>,
        <shengyong1@...wei.com>, <heyunlei@...wei.com>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] f2fs: add fi->commit_lock to protect commit GCed pages

As what I point in last mail, if the atomic file is not committed
yet, gc_data_segment will register_inmem_page the GCed data pages.
This will cause these data pages written twice, the first write
happens in move_data_page->do_write_data_page, and the second
write happens in later __commit_inmem_pages->do_write_data_page.

On 2018/2/9 20:44, Chao Yu wrote:
> On 2018/2/8 11:11, Yunlong Song wrote:
>> Then the GCed data pages are totally mixed with the inmem atomic pages,
> 
> If we add dio_rwsem, GC flow is exclude with atomic write flow. There
> will be not race case to mix GCed page into atomic pages.
> 
> Or you mean:
> 
> 					- gc_data_segment
> 					 - move_data_page
> 					  - f2fs_is_atomic_file
> - f2fs_ioc_start_atomic_write
>   - set_inode_flag(inode, FI_ATOMIC_FILE);
> 					  - f2fs_set_data_page_dirty
> 					   - register_inmem_page
> 
> In this case, GCed page can be mixed into database transaction, but could
> it cause any problem except break rule of isolation for transaction.
> 
>> this will cause the atomic commit ops write the GCed data pages twice
>> (the first write happens in GC).
>>
>> How about using the early two patches to separate the inmem data pages
>> and GCed data pages, and use dio_rwsem instead of this patch to fix the
>> dnode page problem (dnode page commited but data page are not committed
>> for the GCed page)?
> 
> Could we fix the race case first, based on that fixing, and then find the
> place that we can improve?
> 
>>
>>
>> On 2018/2/7 20:16, Chao Yu wrote:
>>> On 2018/2/6 11:49, Yunlong Song wrote:
>>>> This patch adds fi->commit_lock to avoid the case that GCed node pages
>>>> are committed but GCed data pages are not committed. This can avoid the
>>>> db file run into inconsistent state when sudden-power-off happens if
>>>> data pages of atomic file is allowed to be GCed before.
>>>
>>> do_fsync:                GC:
>>> - mutex_lock(&fi->commit_lock);
>>>                      - lock_page()
>>>                       - mutex_lock(&fi->commit_lock);
>>>    - lock_page()
>>>
>>>
>>> Well, please consider lock dependency & code complexity, IMO, reuse
>>> fi->dio_rwsem[WRITE] will be enough as below:
>>>
>>> ---
>>>    fs/f2fs/file.c | 3 +++
>>>    fs/f2fs/gc.c   | 5 -----
>>>    2 files changed, 3 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 672a542e5464..1bdc11feb8d0 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -1711,6 +1711,8 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
>>>
>>>        inode_lock(inode);
>>>
>>> +    down_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
>>> +
>>>        if (f2fs_is_volatile_file(inode))
>>>            goto err_out;
>>>
>>> @@ -1729,6 +1731,7 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
>>>            ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
>>>        }
>>>    err_out:
>>> +    up_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
>>>        inode_unlock(inode);
>>>        mnt_drop_write_file(filp);
>>>        return ret;
>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>> index b9d93fd532a9..e49416283563 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -622,9 +622,6 @@ static void move_data_block(struct inode *inode, block_t bidx,
>>>        if (!check_valid_map(F2FS_I_SB(inode), segno, off))
>>>            goto out;
>>>
>>> -    if (f2fs_is_atomic_file(inode))
>>> -        goto out;
> 
> Seems that we need this check.
> 
>>> -
>>>        if (f2fs_is_pinned_file(inode)) {
>>>            f2fs_pin_file_control(inode, true);
>>>            goto out;
>>> @@ -729,8 +726,6 @@ static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
>>>        if (!check_valid_map(F2FS_I_SB(inode), segno, off))
>>>            goto out;
>>>
>>> -    if (f2fs_is_atomic_file(inode))
>>> -        goto out;
> 
> Ditto.
> 
> Thanks,
> 
>>>        if (f2fs_is_pinned_file(inode)) {
>>>            if (gc_type == FG_GC)
>>>                f2fs_pin_file_control(inode, true);
>>>
>>
> 
> .
> 

-- 
Thanks,
Yunlong Song