linux-kernel - 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

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Date:   Thu, 24 Nov 2022 18:31:02 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Anders Blomdell <anders.blomdell@...trol.lth.se>
CC:     Jeff Layton <jlayton@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.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



> On Nov 23, 2022, at 2:00 PM, Anders Blomdell <anders.blomdell@...trol.lth.se> wrote:
> 
> Make nfsd_splice_actor work with reads with a non-zero offset that doesn't end on a page boundary.
> 
> 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).
> 
> Signed-off-by: Anders Blomdell <anders.blomdell@...trol.lth.se>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2142132
> Fixes: bfbfb6182ad1 "nfsd_splice_actor(): handle compound pages"
> Cc: stable@...r.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=for-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, struct pipe_buffer *buf,
> 		  struct splice_desc *sd)
> {
> 	struct svc_rqst *rqstp = sd->u.data;
> -	struct page *page = buf->page;	// may be a compound one
> +	// buf->page may be a compound one
> 	unsigned offset = buf->offset;
> +	struct page *first = buf->page + offset / PAGE_SIZE;
> +	struct page *last = buf->page + (offset + sd->len - 1) / PAGE_SIZE;
> 
> -	page += offset / PAGE_SIZE;
> -	for (int i = sd->len; i > 0; i -= PAGE_SIZE)
> -		svc_rqst_replace_page(rqstp, page++);
> +	for (struct page *page = first; page <= last; page++)
> +		svc_rqst_replace_page(rqstp, page);
> 	if (rqstp->rq_res.page_len == 0)	// first call
> 		rqstp->rq_res.page_base = offset % PAGE_SIZE;
> 	rqstp->rq_res.page_len += sd->len;
> 
> -- 
> Anders Blomdell                  Email: anders.blomdell@...trol.lth.se
> Department of Automatic Control
> Lund University                  Phone:    +46 46 222 4625
> P.O. Box 118
> SE-221 00 Lund, Sweden

--
Chuck Lever