Re: [f2fs-dev] [PATCH v2] f2fs: fix to avoid mmap vs set_compress_option case

[Chao Yu <chao@kernel.org>]

Jaegeuk,

Any comments on this patch?

On 2023/5/29 18:47, Chao Yu wrote:
> Compression option in inode should not be changed after they have
> been used, however, it may happen in below race case:
> 
> Thread A				Thread B
> - f2fs_ioc_set_compress_option
>   - check f2fs_is_mmap_file()
>   - check get_dirty_pages()
>   - check F2FS_HAS_BLOCKS()
> 					- f2fs_file_mmap
> 					 - set_inode_flag(FI_MMAP_FILE)
> 					- fault
> 					 - do_page_mkwrite
> 					  - f2fs_vm_page_mkwrite
> 					  - f2fs_get_block_locked
> 					 - fault_dirty_shared_page
> 					  - set_page_dirty
>   - update i_compress_algorithm
>   - update i_log_cluster_size
>   - update i_cluster_size
> 
> Avoid such race condition by covering f2fs_file_mmap() w/ inode lock,
> meanwhile add mmap file check condition in f2fs_may_compress() as well.
> 
> Fixes: e1e8debec656 ("f2fs: add F2FS_IOC_SET_COMPRESS_OPTION ioctl")
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
> v2:
> - add mmap file check condition in f2fs_may_compress()
>   fs/f2fs/f2fs.h |  3 ++-
>   fs/f2fs/file.c | 14 +++++++++++---
>   2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 9bd83fb28439..0db8b37c7a4d 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -4487,7 +4487,8 @@ static inline bool f2fs_low_mem_mode(struct f2fs_sb_info *sbi)
>   static inline bool f2fs_may_compress(struct inode *inode)
>   {
>   	if (IS_SWAPFILE(inode) || f2fs_is_pinned_file(inode) ||
> -		f2fs_is_atomic_file(inode) || f2fs_has_inline_data(inode))
> +		f2fs_is_atomic_file(inode) || f2fs_has_inline_data(inode) ||
> +		f2fs_is_mmap_file(inode))
>   		return false;
>   	return S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode);
>   }
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 7b097ab2f5e4..685ded62fc28 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -519,17 +519,25 @@ static loff_t f2fs_llseek(struct file *file, loff_t offset, int whence)
>   static int f2fs_file_mmap(struct file *file, struct vm_area_struct *vma)
>   {
>   	struct inode *inode = file_inode(file);
> +	int ret = 0;
>   
>   	if (unlikely(f2fs_cp_error(F2FS_I_SB(inode))))
>   		return -EIO;
>   
> -	if (!f2fs_is_compress_backend_ready(inode))
> -		return -EOPNOTSUPP;
> +	inode_lock(inode);
> +
> +	if (!f2fs_is_compress_backend_ready(inode)) {
> +		ret = -EOPNOTSUPP;
> +		goto out_unlock;
> +	}
>   
>   	file_accessed(file);
>   	vma->vm_ops = &f2fs_file_vm_ops;
>   	set_inode_flag(inode, FI_MMAP_FILE);
> -	return 0;
> +
> +out_unlock:
> +	inode_unlock(inode);
> +	return ret;
>   }
>   
>   static int f2fs_file_open(struct inode *inode, struct file *filp)


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