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Date:   Thu, 6 May 2021 20:07:39 +0100
From:   "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To:     Vivek Goyal <vgoyal@redhat.com>
Cc:     linux-fsdevel@vger.kernel.org, virtio-fs@redhat.com,
        miklos@szeredi.hu, linux-kernel@vger.kernel.org,
        dan.carpenter@oracle.com
Subject: Re: [PATCH 1/2] virtiofs, dax: Fix smatch warning about loss of info
 during shift
Message-ID: <YJQ+ex2DUPYo1GV5@work-vm>
References: <20210506184304.321645-1-vgoyal@redhat.com>
 <20210506184304.321645-2-vgoyal@redhat.com>
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* Vivek Goyal (vgoyal@redhat.com) wrote:
> Dan reported a smatch warning during potentential loss of info during
> left shift if this code is compiled on 32bit systems.
>=20
> New smatch warnings:
> fs/fuse/dax.c:113 fuse_setup_one_mapping() warn: should 'start_idx << 21'=
 be a
> +64 bit type?
>=20
> I ran smatch and found two more instances of similar warning. This patch
> fixes all such instances.
>=20
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> ---
>  fs/fuse/dax.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>=20
> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> index ff99ab2a3c43..f06fdad3f7b1 100644
> --- a/fs/fuse/dax.c
> +++ b/fs/fuse/dax.c
> @@ -186,7 +186,7 @@ static int fuse_setup_one_mapping(struct inode *inode=
, unsigned long start_idx,
>  	struct fuse_conn_dax *fcd =3D fm->fc->dax;
>  	struct fuse_inode *fi =3D get_fuse_inode(inode);
>  	struct fuse_setupmapping_in inarg;
> -	loff_t offset =3D start_idx << FUSE_DAX_SHIFT;
> +	loff_t offset =3D (loff_t)start_idx << FUSE_DAX_SHIFT;

I've not followed the others back, but isn't it easier to change
the start_idx parameter to be a loff_t, since the places it's called
=66rom are poth loff_t pos?

Dave

>  	FUSE_ARGS(args);
>  	ssize_t err;
> =20
> @@ -872,7 +872,7 @@ static int dmap_writeback_invalidate(struct inode *in=
ode,
>  				     struct fuse_dax_mapping *dmap)
>  {
>  	int ret;
> -	loff_t start_pos =3D dmap->itn.start << FUSE_DAX_SHIFT;
> +	loff_t start_pos =3D (loff_t)dmap->itn.start << FUSE_DAX_SHIFT;
>  	loff_t end_pos =3D (start_pos + FUSE_DAX_SZ - 1);
> =20
>  	ret =3D filemap_fdatawrite_range(inode->i_mapping, start_pos, end_pos);
> @@ -966,7 +966,7 @@ inode_inline_reclaim_one_dmap(struct fuse_conn_dax *f=
cd, struct inode *inode,
>  	dmap =3D inode_lookup_first_dmap(inode);
>  	if (dmap) {
>  		start_idx =3D dmap->itn.start;
> -		dmap_start =3D start_idx << FUSE_DAX_SHIFT;
> +		dmap_start =3D (u64)start_idx << FUSE_DAX_SHIFT;
>  		dmap_end =3D dmap_start + FUSE_DAX_SZ - 1;
>  	}
>  	up_read(&fi->dax->sem);
> @@ -1118,7 +1118,7 @@ static int lookup_and_reclaim_dmap(struct fuse_conn=
_dax *fcd,
>  {
>  	int ret;
>  	struct fuse_inode *fi =3D get_fuse_inode(inode);
> -	loff_t dmap_start =3D start_idx << FUSE_DAX_SHIFT;
> +	loff_t dmap_start =3D (loff_t)start_idx << FUSE_DAX_SHIFT;
>  	loff_t dmap_end =3D (dmap_start + FUSE_DAX_SZ) - 1;
> =20
>  	down_write(&fi->i_mmap_sem);
> --=20
> 2.25.4
>=20
--=20
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK