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

[Chao Yu]

On 2024/3/21 1:42, Daeho Jeong wrote:
> On Wed, Mar 20, 2024 at 2:38 AM Chao Yu <chao@xxxxxxxxxx> wrote:
> > On 2024/3/20 5:23, Daeho Jeong wrote:
> > > From: Daeho Jeong <daehojeong@xxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxx>
> > > ---
> > > 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);