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From:   Daeho Jeong <daeho43@gmail.com>
Date:   Fri, 4 Dec 2020 12:43:23 +0900
Message-ID: <CACOAw_wTFsfgLfrWKRoM1o_HQorJE-=2ztZftQTn+comcpmHxQ@mail.gmail.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix race of pending_pages in decompression
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
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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);
}

2020=EB=85=84 12=EC=9B=94 4=EC=9D=BC (=EA=B8=88) =EC=98=A4=ED=9B=84 12:28, =
Eric Biggers <ebiggers@kernel.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> On Fri, Dec 04, 2020 at 09:58:47AM +0900, Daeho Jeong wrote:
> > diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
> > index 87090da8693d..cdf72e153da0 100644
> > --- a/fs/f2fs/compress.c
> > +++ b/fs/f2fs/compress.c
> > @@ -803,8 +803,6 @@ void f2fs_decompress_pages(struct bio *bio, struct =
page *page, bool verity)
> >       if (cops->destroy_decompress_ctx)
> >               cops->destroy_decompress_ctx(dic);
> >  out_free_dic:
> > -     if (verity)
> > -             atomic_set(&dic->pending_pages, dic->nr_cpages);
> >       if (!verity)
> >               f2fs_decompress_end_io(dic->rpages, dic->cluster_size,
> >                                                               ret, fals=
e);
> > @@ -1498,6 +1496,8 @@ struct decompress_io_ctx *f2fs_alloc_dic(struct c=
ompress_ctx *cc)
> >       dic->magic =3D F2FS_COMPRESSED_PAGE_MAGIC;
> >       dic->inode =3D cc->inode;
> >       atomic_set(&dic->pending_pages, cc->nr_cpages);
> > +     if (fsverity_active(cc->inode))
> > +             atomic_set(&dic->verity_pages, cc->nr_cpages);
> >       dic->cluster_idx =3D cc->cluster_idx;
> >       dic->cluster_size =3D cc->cluster_size;
> >       dic->log_cluster_size =3D cc->log_cluster_size;
>
> The check for fsverity_active() is wrong.  It looks like you need to know
> whether the bio needs to go through the fs-verity data verification.  The
> correct way to determine that is to check whether STEP_VERITY is enabled =
in the
> bio's bio_post_read_ctx.  It's set by f2fs_grab_read_bio() when needed.
>
> - Eric