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Date:   Fri, 30 Sep 2022 06:54:48 +0800
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Subject: Re: [f2fs-dev] [PATCH v2] f2fs: introduce
 F2FS_IOC_START_ATOMIC_REPLACE
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To:     Daeho Jeong <daeho43@gmail.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
References: <20220920014036.2295853-1-daeho43@gmail.com>
 <f4ce9486-f104-b0e2-25ed-f6de96316b76@kernel.org>
 <CACOAw_z=9H6jEQNd8C99c6xO55PJXWJOW7Q=78qtppgysebN2A@mail.gmail.com>
From:   Chao Yu <chao@kernel.org>
In-Reply-To: <CACOAw_z=9H6jEQNd8C99c6xO55PJXWJOW7Q=78qtppgysebN2A@mail.gmail.com>
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On 2022/9/30 0:13, Daeho Jeong wrote:
> On Thu, Sep 29, 2022 at 12:36 AM Chao Yu <chao@kernel.org> wrote:
>>
>> On 2022/9/20 9:40, Daeho Jeong wrote:
>>> From: Daeho Jeong <daehojeong@google.com>
>>>
>>> introduce a new ioctl to replace the whole content of a file atomically,
>>> which means it induces truncate and content update at the same time.
>>> We can start it with F2FS_IOC_START_ATOMIC_REPLACE and complete it with
>>> F2FS_IOC_COMMIT_ATOMIC_WRITE. Or abort it with
>>> F2FS_IOC_ABORT_ATOMIC_WRITE.
>>>
>>> Signed-off-by: Daeho Jeong <daehojeong@google.com>
>>> ---
>>> v2: add undefined ioctl number reported by <lkp@intel.com>
>>> ---
>>>    fs/f2fs/data.c            |  3 +++
>>>    fs/f2fs/f2fs.h            |  1 +
>>>    fs/f2fs/file.c            | 12 ++++++++++--
>>>    fs/f2fs/segment.c         | 14 +++++++++++++-
>>>    include/uapi/linux/f2fs.h |  1 +
>>>    5 files changed, 28 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 6cd29a575105..d3d32db3a25d 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -3438,6 +3438,9 @@ static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi,
>>>        else if (*blk_addr != NULL_ADDR)
>>>                return 0;
>>>
>>> +     if (is_inode_flag_set(inode, FI_ATOMIC_REPLACE))
>>> +             goto reserve_block;
>>> +
>>>        /* Look for the block in the original inode */
>>>        err = __find_data_block(inode, index, &ori_blk_addr);
>>>        if (err)
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 539da7f12cfc..2c49da12d6d8 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -764,6 +764,7 @@ enum {
>>>        FI_COMPRESS_RELEASED,   /* compressed blocks were released */
>>>        FI_ALIGNED_WRITE,       /* enable aligned write */
>>>        FI_COW_FILE,            /* indicate COW file */
>>> +     FI_ATOMIC_REPLACE,      /* indicate atomic replace */
>>>        FI_MAX,                 /* max flag, never be used */
>>>    };
>>>
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 4f9b80c41b1e..4abd9d2a55b3 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -1982,7 +1982,7 @@ static int f2fs_ioc_getversion(struct file *filp, unsigned long arg)
>>>        return put_user(inode->i_generation, (int __user *)arg);
>>>    }
>>>
>>> -static int f2fs_ioc_start_atomic_write(struct file *filp)
>>> +static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
>>>    {
>>>        struct inode *inode = file_inode(filp);
>>>        struct user_namespace *mnt_userns = file_mnt_user_ns(filp);
>>> @@ -2051,6 +2051,12 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>>>
>>>        isize = i_size_read(inode);
>>>        fi->original_i_size = isize;
>>> +     if (truncate) {
>>> +             set_inode_flag(inode, FI_ATOMIC_REPLACE);
>>> +             truncate_inode_pages_final(inode->i_mapping);
>>> +             f2fs_i_size_write(inode, 0);
>>> +             isize = 0;
>>> +     }
>>
>> Hi Daeho,
>>
>> isize should be updated after tagging inode as atomic_write one?
>> otherwise f2fs_mark_inode_dirty_sync() may update isize to inode page,
>> latter checkpoint may persist that change? IIUC...
>>
>> Thanks,
> 
> Hi Chao,
> 
> The first patch of this patchset prevents the inode page from being
> updated as dirty for atomic file cases.
> Is there any other chances for the inode page to be marked as dirty?

I mean:

Thread A				Thread B
- f2fs_ioc_start_atomic_write
  - f2fs_i_size_write(inode, 0)
   - f2fs_mark_inode_dirty_sync
					- checkpoint
					 - persist inode with incorrect zero isize

  - set_inode_flag(inode, FI_ATOMIC_FILE)

Am I missing something?

Thanks,

> 
> Thanks,
> 
>>
>>>        f2fs_i_size_write(fi->cow_inode, isize);
>>>
>>>        spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
>>> @@ -4080,7 +4086,9 @@ static long __f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>>>        case FS_IOC_GETVERSION:
>>>                return f2fs_ioc_getversion(filp, arg);
>>>        case F2FS_IOC_START_ATOMIC_WRITE:
>>> -             return f2fs_ioc_start_atomic_write(filp);
>>> +             return f2fs_ioc_start_atomic_write(filp, false);
>>> +     case F2FS_IOC_START_ATOMIC_REPLACE:
>>> +             return f2fs_ioc_start_atomic_write(filp, true);
>>>        case F2FS_IOC_COMMIT_ATOMIC_WRITE:
>>>                return f2fs_ioc_commit_atomic_write(filp);
>>>        case F2FS_IOC_ABORT_ATOMIC_WRITE:
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 143b7ea0fb8e..c524538a9013 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -263,14 +263,26 @@ static void __complete_revoke_list(struct inode *inode, struct list_head *head,
>>>                                        bool revoke)
>>>    {
>>>        struct revoke_entry *cur, *tmp;
>>> +     pgoff_t start_index = 0;
>>> +     bool truncate = is_inode_flag_set(inode, FI_ATOMIC_REPLACE);
>>>
>>>        list_for_each_entry_safe(cur, tmp, head, list) {
>>> -             if (revoke)
>>> +             if (revoke) {
>>>                        __replace_atomic_write_block(inode, cur->index,
>>>                                                cur->old_addr, NULL, true);
>>> +             } else if (truncate) {
>>> +                     f2fs_truncate_hole(inode, start_index, cur->index);
>>> +                     start_index = cur->index + 1;
>>> +             }
>>> +
>>>                list_del(&cur->list);
>>>                kmem_cache_free(revoke_entry_slab, cur);
>>>        }
>>> +
>>> +     if (!revoke && truncate) {
>>> +             f2fs_do_truncate_blocks(inode, start_index * PAGE_SIZE, false);
>>> +             clear_inode_flag(inode, FI_ATOMIC_REPLACE);
>>> +     }
>>>    }
>>>
>>>    static int __f2fs_commit_atomic_write(struct inode *inode)
>>> diff --git a/include/uapi/linux/f2fs.h b/include/uapi/linux/f2fs.h
>>> index 3121d127d5aa..955d440be104 100644
>>> --- a/include/uapi/linux/f2fs.h
>>> +++ b/include/uapi/linux/f2fs.h
>>> @@ -42,6 +42,7 @@
>>>                                                struct f2fs_comp_option)
>>>    #define F2FS_IOC_DECOMPRESS_FILE    _IO(F2FS_IOCTL_MAGIC, 23)
>>>    #define F2FS_IOC_COMPRESS_FILE              _IO(F2FS_IOCTL_MAGIC, 24)
>>> +#define F2FS_IOC_START_ATOMIC_REPLACE        _IO(F2FS_IOCTL_MAGIC, 25)
>>>
>>>    /*
>>>     * should be same as XFS_IOC_GOINGDOWN.