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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Anders Blomdell <anders.blomdell@control.lth.se>
CC:     Jeff Layton <jlayton@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v2 1/1] Make nfsd_splice_actor work with reads with a
 non-zero offset that doesn't end on a page boundary
Thread-Topic: [PATCH v2 1/1] Make nfsd_splice_actor work with reads with a
 non-zero offset that doesn't end on a page boundary
Thread-Index: AQHY/239SEcVcSHvz0mNdsR515WWZ65OZvKA
Date:   Thu, 24 Nov 2022 18:31:02 +0000
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> On Nov 23, 2022, at 2:00 PM, Anders Blomdell <anders.blomdell@control.lth=
.se> wrote:
>=20
> Make nfsd_splice_actor work with reads with a non-zero offset that doesn'=
t end on a page boundary.
>=20
> This was found when virtual machines with nfs-mounted qcow2 disks failed =
to boot properly (originally found
> on v6.0.5, fix also needed and tested on v6.0.9 and v6.1-rc6).
>=20
> Signed-off-by: Anders Blomdell <anders.blomdell@control.lth.se>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=3D2142132
> Fixes: bfbfb6182ad1 "nfsd_splice_actor(): handle compound pages"
> Cc: stable@vger.kernel.org # v6.0+

"b4 am" and other tooling failed to recognize the diff content in
this email, so I've applied Al's version to nfsd's for-rc, after
running some regression tests. See:

https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/log/?h=3Dfor-=
rc

I will see that a pull request is sent to Linus before 6.1-rc7.

Thanks for reporting and chasing this down.


> -- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -869,12 +869,13 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, str=
uct pipe_buffer *buf,
> 		  struct splice_desc *sd)
> {
> 	struct svc_rqst *rqstp =3D sd->u.data;
> -	struct page *page =3D buf->page;	// may be a compound one
> +	// buf->page may be a compound one
> 	unsigned offset =3D buf->offset;
> +	struct page *first =3D buf->page + offset / PAGE_SIZE;
> +	struct page *last =3D buf->page + (offset + sd->len - 1) / PAGE_SIZE;
>=20
> -	page +=3D offset / PAGE_SIZE;
> -	for (int i =3D sd->len; i > 0; i -=3D PAGE_SIZE)
> -		svc_rqst_replace_page(rqstp, page++);
> +	for (struct page *page =3D first; page <=3D last; page++)
> +		svc_rqst_replace_page(rqstp, page);
> 	if (rqstp->rq_res.page_len =3D=3D 0)	// first call
> 		rqstp->rq_res.page_base =3D offset % PAGE_SIZE;
> 	rqstp->rq_res.page_len +=3D sd->len;
>=20
> --=20
> Anders Blomdell                  Email: anders.blomdell@control.lth.se
> Department of Automatic Control
> Lund University                  Phone:    +46 46 222 4625
> P.O. Box 118
> SE-221 00 Lund, Sweden

--
Chuck Lever