Re: [f2fs-dev] [PATCH] f2fs: fix race of pending_pages in decompression

[Eric Biggers]

On Fri, Dec 04, 2020 at 12:43:23PM +0900, Daeho Jeong wrote:
> STEP_VERITY is enabled by f2fs_need_verity() and the function is like below.
> We already know the second condition (idx < DIV_ROUND_UP...) is
> satisfied when invoking f2fs_alloc_dic().
> 
> static inline bool f2fs_need_verity(const struct inode *inode, pgoff_t idx)
> {
>         return fsverity_active(inode) &&
>                idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
> }

Are you sure?  I thought that compression (and encryption) apply to the whole
file, including any Merkle tree blocks past i_size.

Also, even if you include the i_size check, it's still wrong to check
fsverity_active() in the middle of the I/O because FS_IOC_ENABLE_VERITY can
execute concurrently, causing fsverity_active() to return false at the beginning
of the I/O and true later in the I/O.  It needs to be checked only once, at the
beginning...

- Eric