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Subject: Re: [PATCH 1/5] nfsd: only call inode_query_iversion in the I_VERSION
 case
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <1606765137-17257-1-git-send-email-bfields@fieldses.org>
Date:   Mon, 30 Nov 2020 16:03:23 -0500
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Bruce Fields <bfields@redhat.com>
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Message-Id: <50CF0FBE-9C58-4DAA-B524-DE15047E9FD1@oracle.com>
References: <1606765137-17257-1-git-send-email-bfields@fieldses.org>
To:     Bruce Fields <bfields@fieldses.org>
Precedence: bulk


> On Nov 30, 2020, at 2:38 PM, J. Bruce Fields <bfields@fieldses.org> =
wrote:
>=20
> From: "J. Bruce Fields" <bfields@redhat.com>
>=20
> inode_query_iversion() can modify i_version.  Depending on the =
exported
> filesystem, that may not be safe.  For example, if you're re-exporting
> NFS, NFS stores the server's change attribute in i_version and does =
not
> expect it to be modified locally.  This has been observed causing
> unnecessary cache invalidations.
>=20
> The way a filesystem indicates that it's OK to call
> inode_query_iverson() is by setting SB_I_VERSION.
>=20
> So, move the I_VERSION check out of encode_change(), where it's used
> only in FATTR responses, to nfsd4_changeattr(), which is also called =
for
> pre- and post- operation attributes.
>=20
> (Note we could also pull the NFSEXP_V4ROOT case into
> nfsd4_change_attribute as well.  That would actually be a no-op, since
> pre/post attrs are only used for metadata-modifying operations, and
> V4ROOT exports are read-only.  But we might make the change in the
> future just for simplicity.)
>=20
> Reported-by: Daire Byrne <daire@dneg.com>
> Signed-off-by: J. Bruce Fields <bfields@redhat.com>

New sparse warnings after this one is applied:

/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:270:24: warning: incorrect =
type in assignment (different base types)
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:270:24:    expected unsigned =
long long [assigned] [usertype] chattr
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:270:24:    got restricted =
__be32 [usertype]
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:272:24: warning: invalid =
assignment: +=3D
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:272:24:    left side has type =
unsigned long long
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:272:24:    right side has type =
restricted __be32
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:270:24: warning: incorrect =
type in assignment (different base types)
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:270:24:    expected unsigned =
long long [assigned] [usertype] chattr
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:270:24:    got restricted =
__be32 [usertype]
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:272:24: warning: invalid =
assignment: +=3D
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:272:24:    left side has type =
unsigned long long
/home/cel/src/linux/linux/fs/nfsd/nfsfh.h:272:24:    right side has type =
restricted __be32


> ---
> fs/nfsd/nfs3xdr.c |  5 ++---
> fs/nfsd/nfs4xdr.c |  6 +-----
> fs/nfsd/nfsfh.h   | 14 ++++++++++----
> 3 files changed, 13 insertions(+), 12 deletions(-)
>=20
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index 2277f83da250..dfbf390ff40c 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -291,14 +291,13 @@ void fill_post_wcc(struct svc_fh *fhp)
> 		printk("nfsd: inode locked twice during operation.\n");
>=20
> 	err =3D fh_getattr(fhp, &fhp->fh_post_attr);
> -	fhp->fh_post_change =3D =
nfsd4_change_attribute(&fhp->fh_post_attr,
> -						     =
d_inode(fhp->fh_dentry));
> 	if (err) {
> 		fhp->fh_post_saved =3D false;
> -		/* Grab the ctime anyway - set_change_info might use it =
*/
> 		fhp->fh_post_attr.ctime =3D =
d_inode(fhp->fh_dentry)->i_ctime;
> 	} else
> 		fhp->fh_post_saved =3D true;
> +	fhp->fh_post_change =3D =
nfsd4_change_attribute(&fhp->fh_post_attr,
> +						     =
d_inode(fhp->fh_dentry));
> }
>=20
> /*
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index 833a2c64dfe8..56fd5f6d5c44 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -2298,12 +2298,8 @@ static __be32 *encode_change(__be32 *p, struct =
kstat *stat, struct inode *inode,
> 	if (exp->ex_flags & NFSEXP_V4ROOT) {
> 		*p++ =3D =
cpu_to_be32(convert_to_wallclock(exp->cd->flush_time));
> 		*p++ =3D 0;
> -	} else if (IS_I_VERSION(inode)) {
> +	} else
> 		p =3D xdr_encode_hyper(p, nfsd4_change_attribute(stat, =
inode));
> -	} else {
> -		*p++ =3D cpu_to_be32(stat->ctime.tv_sec);
> -		*p++ =3D cpu_to_be32(stat->ctime.tv_nsec);
> -	}
> 	return p;
> }
>=20
> diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
> index 56cfbc361561..3faf5974fa4e 100644
> --- a/fs/nfsd/nfsfh.h
> +++ b/fs/nfsd/nfsfh.h
> @@ -261,10 +261,16 @@ static inline u64 nfsd4_change_attribute(struct =
kstat *stat,
> {
> 	u64 chattr;
>=20
> -	chattr =3D  stat->ctime.tv_sec;
> -	chattr <<=3D 30;
> -	chattr +=3D stat->ctime.tv_nsec;
> -	chattr +=3D inode_query_iversion(inode);
> +	if (IS_I_VERSION(inode)) {
> +		chattr =3D  stat->ctime.tv_sec;
> +		chattr <<=3D 30;
> +		chattr +=3D stat->ctime.tv_nsec;
> +		chattr +=3D inode_query_iversion(inode);
> +	} else {
> +		chattr =3D cpu_to_be32(stat->ctime.tv_sec);
> +		chattr <<=3D 32;
> +		chattr +=3D cpu_to_be32(stat->ctime.tv_nsec);
> +	}
> 	return chattr;
> }
>=20
> --=20
> 2.28.0
>=20

--
Chuck Lever