linux-kernel - Re: [f2fs-dev] [PATCH v3] f2fs: prevent writing without fallocate() for pinned files

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Date: Sat, 23 Mar 2024 12:26:47 +0800
From: Chao Yu <chao@...nel.org>
To: Daeho Jeong <daeho43@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
 kernel-team@...roid.com, Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: prevent writing without fallocate()
 for pinned files

On 2024/3/21 1:42, Daeho Jeong wrote:
> On Wed, Mar 20, 2024 at 2:38 AM Chao Yu <chao@...nel.org> wrote:
>>
>> On 2024/3/20 5:23, Daeho Jeong wrote:
>>> From: Daeho Jeong <daehojeong@...gle.com>
>>>
>>> In a case writing without fallocate(), we can't guarantee it's allocated
>>> in the conventional area for zoned stroage.
>>>
>>> Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
>>> ---
>>> v2: covered the direct io case
>>> v3: covered the mkwrite case
>>> ---
>>>    fs/f2fs/data.c | 14 ++++++++++++--
>>>    fs/f2fs/file.c | 16 ++++++++--------
>>>    2 files changed, 20 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index c21b92f18463..d3e5ab2736a6 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -1584,8 +1584,11 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>>>
>>>        /* use out-place-update for direct IO under LFS mode */
>>>        if (map->m_may_create &&
>>> -         (is_hole || (f2fs_lfs_mode(sbi) && flag == F2FS_GET_BLOCK_DIO))) {
>>> -             if (unlikely(f2fs_cp_error(sbi))) {
>>> +         (is_hole || (f2fs_lfs_mode(sbi) && flag == F2FS_GET_BLOCK_DIO &&
>>> +                      !f2fs_is_pinned_file(inode)))) {
>>> +             if (unlikely(f2fs_cp_error(sbi)) ||
>>> +                 (f2fs_is_pinned_file(inode) && is_hole &&
>>> +                  flag != F2FS_GET_BLOCK_PRE_DIO)) {
>>>                        err = -EIO;
>>>                        goto sync_out;
>>>                }
>>> @@ -3378,6 +3381,8 @@ static int prepare_write_begin(struct f2fs_sb_info *sbi,
>>>                f2fs_map_lock(sbi, flag);
>>>                locked = true;
>>>        } else if ((pos & PAGE_MASK) >= i_size_read(inode)) {
>>> +             if (f2fs_is_pinned_file(inode))
>>> +                     return -EIO;
>>>                f2fs_map_lock(sbi, flag);
>>>                locked = true;
>>>        }
>>> @@ -3407,6 +3412,11 @@ static int prepare_write_begin(struct f2fs_sb_info *sbi,
>>>
>>>        if (!f2fs_lookup_read_extent_cache_block(inode, index,
>>>                                                 &dn.data_blkaddr)) {
>>> +             if (f2fs_is_pinned_file(inode)) {
>>> +                     err = -EIO;
>>> +                     goto out;
>>> +             }
>>> +
>>>                if (locked) {
>>>                        err = f2fs_reserve_block(&dn, index);
>>>                        goto out;
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 82277e95c88f..4db3b21c804b 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -57,7 +57,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>>>        struct inode *inode = file_inode(vmf->vma->vm_file);
>>>        struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>>        struct dnode_of_data dn;
>>> -     bool need_alloc = true;
>>> +     bool need_alloc = !f2fs_is_pinned_file(inode);
>>
>> Will this check races w/ pinfile get|set?
> 
> Do you mean "set/clear" case? I believe "set" case is okay, since we

Yup,

> can't set if the inode already has a data block. For "clear" case, I

However, we can set pinfile on written inode in regular block device:

	if (f2fs_sb_has_blkzoned(sbi) && F2FS_HAS_BLOCKS(inode)) {
		ret = -EFBIG;
		goto out;
	}

Should we add the logic only if blkzoned feture is enabled?

> believe mkwrite failure is okay in racy conditions caused by clearing
> the pin flag. What do you think?

Or we can use filemap_invalidate_lock() in f2fs_ioc_set_pin_file() to
avoid the race condition?

Thanks,

> 
>>
>> Thanks,
>>
>>>        int err = 0;
>>>        vm_fault_t ret;
>>>
>>> @@ -114,19 +114,15 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>>>                goto out_sem;
>>>        }
>>>
>>> +     set_new_dnode(&dn, inode, NULL, NULL, 0);
>>>        if (need_alloc) {
>>>                /* block allocation */
>>> -             set_new_dnode(&dn, inode, NULL, NULL, 0);
>>>                err = f2fs_get_block_locked(&dn, page->index);
>>> -     }
>>> -
>>> -#ifdef CONFIG_F2FS_FS_COMPRESSION
>>> -     if (!need_alloc) {
>>> -             set_new_dnode(&dn, inode, NULL, NULL, 0);
>>> +     } else {
>>>                err = f2fs_get_dnode_of_data(&dn, page->index, LOOKUP_NODE);
>>>                f2fs_put_dnode(&dn);
>>>        }
>>> -#endif
>>> +
>>>        if (err) {
>>>                unlock_page(page);
>>>                goto out_sem;
>>> @@ -4611,6 +4607,10 @@ static int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *iter,
>>>                        return ret;
>>>        }
>>>
>>> +     /* For pinned files, it should be fallocate()-ed in advance. */
>>> +     if (f2fs_is_pinned_file(inode))
>>> +             return 0;
>>> +
>>>        /* Do not preallocate blocks that will be written partially in 4KB. */
>>>        map.m_lblk = F2FS_BLK_ALIGN(pos);
>>>        map.m_len = F2FS_BYTES_TO_BLK(pos + count);