[PATCH v2 1/1] Make nfsd_splice_actor work with reads with a non-zero offset that doesn't end on a page boundary

[PATCH v2 1/1] Make nfsd_splice_actor work with reads with a non-zero offset that doesn't end on a page boundary

[Anders Blomdell]

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@control.lth.se>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2142132
Fixes: bfbfb6182ad1 "nfsd_splice_actor(): handle compound pages"
Cc: stable@vger.kernel.org # v6.0+

-- 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@control.lth.se
Department of Automatic Control
Lund University                  Phone:    +46 46 222 4625
P.O. Box 118
SE-221 00 Lund, Sweden

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

[Chuck Lever III]

> On Nov 23, 2022, at 2:00 PM, Anders Blomdell <anders.blomdell@control.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@control.lth.se>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2142132
> 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=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@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