Re: [f2fs-dev] [PATCH] f2fs: prevent atomic file from being dirtied before commit

[Chao Yu <chao@kernel.org>]

On 2024/9/4 10:52, Daeho Jeong wrote:
> On Tue, Sep 3, 2024 at 7:26 PM Chao Yu <chao@kernel.org> wrote:
>>
>> On 2024/9/4 1:07, Daeho Jeong wrote:
>>> On Mon, Sep 2, 2024 at 3:08 AM Chao Yu <chao@kernel.org> wrote:
>>>>
>>>> On 2024/8/27 4:23, Daeho Jeong wrote:
>>>>> From: Daeho Jeong <daehojeong@google.com>
>>>>>
>>>>> Keep atomic file clean while updating and make it dirtied during commit
>>>>> in order to avoid unnecessary and excessive inode updates in the previous
>>>>> fix.
>>>>>
>>>>> Fixes: 4bf78322346f ("f2fs: mark inode dirty for FI_ATOMIC_COMMITTED flag")
>>>>> Signed-off-by: Daeho Jeong <daehojeong@google.com>
>>>>> ---
>>>>>     fs/f2fs/f2fs.h    |  3 +--
>>>>>     fs/f2fs/inode.c   | 10 ++++++----
>>>>>     fs/f2fs/segment.c | 10 ++++++++--
>>>>>     3 files changed, 15 insertions(+), 8 deletions(-)
>>>>>
>>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>>> index 465b2fd50c70..5a7f6fa8b585 100644
>>>>> --- a/fs/f2fs/f2fs.h
>>>>> +++ b/fs/f2fs/f2fs.h
>>>>> @@ -801,7 +801,7 @@ enum {
>>>>>         FI_COMPRESS_RELEASED,   /* compressed blocks were released */
>>>>>         FI_ALIGNED_WRITE,       /* enable aligned write */
>>>>>         FI_COW_FILE,            /* indicate COW file */
>>>>> -     FI_ATOMIC_COMMITTED,    /* indicate atomic commit completed except disk sync */
>>>>> +     FI_ATOMIC_DIRTIED,      /* indicate atomic file is dirtied */
>>>>>         FI_ATOMIC_REPLACE,      /* indicate atomic replace */
>>>>>         FI_OPENED_FILE,         /* indicate file has been opened */
>>>>>         FI_MAX,                 /* max flag, never be used */
>>>>> @@ -3042,7 +3042,6 @@ static inline void __mark_inode_dirty_flag(struct inode *inode,
>>>>>         case FI_INLINE_DOTS:
>>>>>         case FI_PIN_FILE:
>>>>>         case FI_COMPRESS_RELEASED:
>>>>> -     case FI_ATOMIC_COMMITTED:
>>>>>                 f2fs_mark_inode_dirty_sync(inode, true);
>>>>>         }
>>>>>     }
>>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>>>>> index 1eb250c6b392..5dd3e55d2be2 100644
>>>>> --- a/fs/f2fs/inode.c
>>>>> +++ b/fs/f2fs/inode.c
>>>>> @@ -35,6 +35,11 @@ void f2fs_mark_inode_dirty_sync(struct inode *inode, bool sync)
>>>>>         if (f2fs_inode_dirtied(inode, sync))
>>>>
>>>> It will return directly here if inode was dirtied, so it may missed to set
>>>> FI_ATOMIC_DIRTIED flag?
>>>
>>> Is it possible for it to be already dirty, since we already made it
>>> clean with f2fs_write_inode() when we started the atomic write?
>>
>> Some ioctl interfaces may race w/ atomic write? e.g. set_pin_file won't
>> check atomic_file status, and may dirty inode after we started atomic
>> write, so we'd better detect such race condition and break ioctl to
>> avoid ruin atomic write? and maybe we can add f2fs_bug_on() in
>> f2fs_mark_inode_dirty_sync() to detect any other missing cases?
>>
> 
> How about exchanging the positions of f2fs_write_inode() and
> set_inode_flag() in f2fs_ioc_start_atomic_write()?
> 
> ...
>          f2fs_write_inode(inode, NULL);
> 
>          stat_inc_atomic_inode(inode);
> 
>          set_inode_flag(inode, FI_ATOMIC_FILE);
> ...

Oh, I'm not sure I've got your point, after exchanging we still may suffer
below race condition, right?

- f2fs_ioc_start_atomic_write
  - set_inode_flag(inode, FI_ATOMIC_FILE)
  - f2fs_write_inode(inode, NULL)
					- f2fs_ioc_set_pin_file
					 - set_inode_flag(inode, FI_PIN_FILE)
					  - __mark_inode_dirty_flag()
- f2fs_ioc_commit_atomic_write

So that I proposed a fix for this:
https://lore.kernel.org/linux-f2fs-devel/20240904032047.1264706-1-chao@kernel.org

Thanks,

> 
>> Thanks,
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>                 return;
>>>>>
>>>>> +     if (f2fs_is_atomic_file(inode)) {
>>>>> +             set_inode_flag(inode, FI_ATOMIC_DIRTIED);
>>>>> +             return;
>>>>> +     }
>>>>> +
>>>>>         mark_inode_dirty_sync(inode);
>>>>>     }
>>>>>
>>>>> @@ -653,10 +658,7 @@ void f2fs_update_inode(struct inode *inode, struct page *node_page)
>>>>>         ri->i_gid = cpu_to_le32(i_gid_read(inode));
>>>>>         ri->i_links = cpu_to_le32(inode->i_nlink);
>>>>>         ri->i_blocks = cpu_to_le64(SECTOR_TO_BLOCK(inode->i_blocks) + 1);
>>>>> -
>>>>> -     if (!f2fs_is_atomic_file(inode) ||
>>>>> -                     is_inode_flag_set(inode, FI_ATOMIC_COMMITTED))
>>>>> -             ri->i_size = cpu_to_le64(i_size_read(inode));
>>>>> +     ri->i_size = cpu_to_le64(i_size_read(inode));
>>>>>
>>>>>         if (et) {
>>>>>                 read_lock(&et->lock);
>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>>> index 78c3198a6308..2b5391b229a8 100644
>>>>> --- a/fs/f2fs/segment.c
>>>>> +++ b/fs/f2fs/segment.c
>>>>> @@ -196,9 +196,12 @@ void f2fs_abort_atomic_write(struct inode *inode, bool clean)
>>>>>                 truncate_inode_pages_final(inode->i_mapping);
>>>>>
>>>>>         release_atomic_write_cnt(inode);
>>>>> -     clear_inode_flag(inode, FI_ATOMIC_COMMITTED);
>>>>>         clear_inode_flag(inode, FI_ATOMIC_REPLACE);
>>>>>         clear_inode_flag(inode, FI_ATOMIC_FILE);
>>>>> +     if (is_inode_flag_set(inode, FI_ATOMIC_DIRTIED)) {
>>>>> +             clear_inode_flag(inode, FI_ATOMIC_DIRTIED);
>>>>> +             f2fs_mark_inode_dirty_sync(inode, true);
>>>>> +     }
>>>>>         stat_dec_atomic_inode(inode);
>>>>>
>>>>>         F2FS_I(inode)->atomic_write_task = NULL;
>>>>> @@ -365,7 +368,10 @@ static int __f2fs_commit_atomic_write(struct inode *inode)
>>>>>                 sbi->revoked_atomic_block += fi->atomic_write_cnt;
>>>>>         } else {
>>>>>                 sbi->committed_atomic_block += fi->atomic_write_cnt;
>>>>> -             set_inode_flag(inode, FI_ATOMIC_COMMITTED);
>>>>> +             if (is_inode_flag_set(inode, FI_ATOMIC_DIRTIED)) {
>>>>> +                     clear_inode_flag(inode, FI_ATOMIC_DIRTIED);
>>>>> +                     f2fs_mark_inode_dirty_sync(inode, true);
>>>>> +             }
>>>>>         }
>>>>>
>>>>>         __complete_revoke_list(inode, &revoke_list, ret ? true : false);
>>>>
>>