On Tue, Jul 16, 2024 at 2:46 PM Ofir Gal <ofir.gal@xxxxxxxxxxx> wrote:
>
> Xiubo/Ilya please take a look
>
> On 6/11/24 09:36, Ofir Gal wrote:
> > Currently ceph_tcp_sendpage() and do_try_sendpage() use sendpage_ok() in
> > order to enable MSG_SPLICE_PAGES, it check the first page of the
> > iterator, the iterator may represent contiguous pages.
> >
> > MSG_SPLICE_PAGES enables skb_splice_from_iter() which checks all the
> > pages it sends with sendpage_ok().
> >
> > When ceph_tcp_sendpage() or do_try_sendpage() send an iterator that the
> > first page is sendable, but one of the other pages isn't
> > skb_splice_from_iter() warns and aborts the data transfer.
> >
> > Using the new helper sendpages_ok() in order to enable MSG_SPLICE_PAGES
> > solves the issue.
> >
> > Signed-off-by: Ofir Gal <ofir.gal@xxxxxxxxxxx>
> > ---
> > net/ceph/messenger_v1.c | 2 +-
> > net/ceph/messenger_v2.c | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ceph/messenger_v1.c b/net/ceph/messenger_v1.c
> > index 0cb61c76b9b8..a6788f284cd7 100644
> > --- a/net/ceph/messenger_v1.c
> > +++ b/net/ceph/messenger_v1.c
> > @@ -94,7 +94,7 @@ static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
> > * coalescing neighboring slab objects into a single frag which
> > * triggers one of hardened usercopy checks.
> > */
> > - if (sendpage_ok(page))
> > + if (sendpages_ok(page, size, offset))
> > msg.msg_flags |= MSG_SPLICE_PAGES;
> >
> > bvec_set_page(&bvec, page, size, offset);
> > diff --git a/net/ceph/messenger_v2.c b/net/ceph/messenger_v2.c
> > index bd608ffa0627..27f8f6c8eb60 100644
> > --- a/net/ceph/messenger_v2.c
> > +++ b/net/ceph/messenger_v2.c
> > @@ -165,7 +165,7 @@ static int do_try_sendpage(struct socket *sock, struct iov_iter *it)
> > * coalescing neighboring slab objects into a single frag
> > * which triggers one of hardened usercopy checks.
> > */
> > - if (sendpage_ok(bv.bv_page))
> > + if (sendpages_ok(bv.bv_page, bv.bv_len, bv.bv_offset))
> > msg.msg_flags |= MSG_SPLICE_PAGES;
> > else
> > msg.msg_flags &= ~MSG_SPLICE_PAGES;
>
Hi Ofir,
Ceph should be fine as is -- there is an internal "cursor" abstraction
that that is limited to PAGE_SIZE chunks, using bvec_iter_bvec() instead
of mp_bvec_iter_bvec(), etc. This means that both do_try_sendpage() and
ceph_tcp_sendpage() should be called only with
page_off + len <= PAGE_SIZE
being true even if the page is contiguous (and that we lose out on the
potential performance benefit, of course...).
That said, if the plan is to remove sendpage_ok() so that it doesn't
accidentally grow new users who are unaware of this pitfall, consider
this
Acked-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Thanks,
Ilya
