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Message-ID: <CAOi1vP_g70kV_YFjHNoS1hHPpCiMxW1hTfm92Ud35ehYrmv=1Q@mail.gmail.com>
Date: Mon, 26 Jun 2023 22:22:51 +0200
From: Ilya Dryomov <idryomov@...il.com>
To: David Howells <dhowells@...hat.com>
Cc: netdev@...r.kernel.org, Xiubo Li <xiubli@...hat.com>,
Jeff Layton <jlayton@...nel.org>, "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Jens Axboe <axboe@...nel.dk>, Matthew Wilcox <willy@...radead.org>, ceph-devel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] libceph: Partially revert changes to support MSG_SPLICE_PAGES
On Mon, Jun 26, 2023 at 7:53 PM David Howells <dhowells@...hat.com> wrote:
>
>
> Fix the mishandling of MSG_DONTWAIT and also reinstates the per-page
> checking of the source pages (which might have come from a DIO write by
> userspace) by partially reverting the changes to support MSG_SPLICE_PAGES
> and doing things a little differently. In messenger_v1:
>
> (1) The ceph_tcp_sendpage() is resurrected and the callers reverted to use
> that.
>
> (2) The callers now pass MSG_MORE unconditionally. Previously, they were
> passing in MSG_MORE|MSG_SENDPAGE_NOTLAST and then degrading that to
> just MSG_MORE on the last call to ->sendpage().
>
> (3) Make ceph_tcp_sendpage() a wrapper around sendmsg() rather than
> sendpage(), setting MSG_SPLICE_PAGES if sendpage_ok() returns true on
> the page.
>
> In messenger_v2:
>
> (4) Bring back do_try_sendpage() and make the callers use that.
>
> (5) Make do_try_sendpage() use sendmsg() for both cases and set
> MSG_SPLICE_PAGES if sendpage_ok() is set.
>
> Note that libceph is using sendpage_ok() for this, but it should not really
> be considered exhaustive in this regard - this is, however, what libceph is
> doing upstream.
Such use spans far beyond libceph: drbd, iSCSI, NVMe-over-TCP, etc.
sendpage_ok() the only tool we have got...
>
> Fixes: 40a8c17aa770 ("ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage")
> Fixes: fa094ccae1e7 ("ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()")
> Reported-by: Ilya Dryomov <idryomov@...il.com>
> Link: https://lore.kernel.org/r/CAOi1vP9vjLfk3W+AJFeexC93jqPaPUn2dD_4NrzxwoZTbYfOnw@mail.gmail.com/
> Link: https://lore.kernel.org/r/CAOi1vP_Bn918j24S94MuGyn+Gxk212btw7yWeDrRcW1U8pc_BA@mail.gmail.com/
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Ilya Dryomov <idryomov@...il.com>
> cc: Xiubo Li <xiubli@...hat.com>
> cc: Jeff Layton <jlayton@...nel.org>
> cc: "David S. Miller" <davem@...emloft.net>
> cc: Eric Dumazet <edumazet@...gle.com>
> cc: Jakub Kicinski <kuba@...nel.org>
> cc: Paolo Abeni <pabeni@...hat.com>
> cc: Jens Axboe <axboe@...nel.dk>
> cc: Matthew Wilcox <willy@...radead.org>
> cc: ceph-devel@...r.kernel.org
> cc: netdev@...r.kernel.org
> ---
> net/ceph/messenger_v1.c | 57 +++++++++++++++++++------------
> net/ceph/messenger_v2.c | 87 ++++++++++++++++++++++++++++++++++++++----------
> 2 files changed, 105 insertions(+), 39 deletions(-)
>
> diff --git a/net/ceph/messenger_v1.c b/net/ceph/messenger_v1.c
> index 814579f27f04..1ee58cbaf151 100644
> --- a/net/ceph/messenger_v1.c
> +++ b/net/ceph/messenger_v1.c
> @@ -74,6 +74,38 @@ static int ceph_tcp_sendmsg(struct socket *sock, struct kvec *iov,
> return r;
> }
>
> +/*
> + * @more: either or both of MSG_MORE and MSG_SENDPAGE_NOTLAST
MSG_SENDPAGE_NOTLAST flag doesn't exist anymore.
> + */
> +static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
> + int offset, size_t size, int more)
> +{
> + struct msghdr msg = {
> + .msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL | more,
> + };
> + struct bio_vec bvec;
> + int ret;
> +
> + /*
> + * sendpage cannot properly handle pages with page_count == 0,
I would suggest sendpage -> MSG_SPLICE_PAGES here like was done in
the other file.
> + * we need to fall back to sendmsg if that's the case.
> + *
> + * Same goes for slab pages: skb_can_coalesce() allows
> + * coalescing neighboring slab objects into a single frag which
> + * triggers one of hardened usercopy checks.
> + */
> + if (sendpage_ok(page))
> + msg.msg_flags |= MSG_SPLICE_PAGES;
> +
> + bvec_set_page(&bvec, page, size, offset);
The bvec is not added to the message, so I don't think this actually
sends anything...
> +
> + ret = sock_sendmsg(sock, &msg);
> + if (ret == -EAGAIN)
> + ret = 0;
> +
> + return ret;
> +}
> +
> static void con_out_kvec_reset(struct ceph_connection *con)
> {
> BUG_ON(con->v1.out_skip);
> @@ -450,10 +482,6 @@ static int write_partial_message_data(struct ceph_connection *con)
> */
> crc = do_datacrc ? le32_to_cpu(msg->footer.data_crc) : 0;
> while (cursor->total_resid) {
> - struct bio_vec bvec;
> - struct msghdr msghdr = {
> - .msg_flags = MSG_SPLICE_PAGES,
> - };
> struct page *page;
> size_t page_offset;
> size_t length;
> @@ -465,13 +493,8 @@ static int write_partial_message_data(struct ceph_connection *con)
> }
>
> page = ceph_msg_data_next(cursor, &page_offset, &length);
> - if (length != cursor->total_resid)
> - msghdr.msg_flags |= MSG_MORE;
> -
> - bvec_set_page(&bvec, page, length, page_offset);
> - iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, length);
> -
> - ret = sock_sendmsg(con->sock, &msghdr);
> + ret = ceph_tcp_sendpage(con->sock, page, page_offset, length,
> + MSG_MORE);
> if (ret <= 0) {
> if (do_datacrc)
> msg->footer.data_crc = cpu_to_le32(crc);
> @@ -501,22 +524,14 @@ static int write_partial_message_data(struct ceph_connection *con)
> */
> static int write_partial_skip(struct ceph_connection *con)
> {
> - struct bio_vec bvec;
> - struct msghdr msghdr = {
> - .msg_flags = MSG_SPLICE_PAGES | MSG_MORE,
> - };
> int ret;
>
> dout("%s %p %d left\n", __func__, con, con->v1.out_skip);
> while (con->v1.out_skip > 0) {
> size_t size = min(con->v1.out_skip, (int)PAGE_SIZE);
>
> - if (size == con->v1.out_skip)
> - msghdr.msg_flags &= ~MSG_MORE;
> - bvec_set_page(&bvec, ZERO_PAGE(0), size, 0);
> - iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, size);
> -
> - ret = sock_sendmsg(con->sock, &msghdr);
> + ret = ceph_tcp_sendpage(con->sock, ceph_zero_page, 0, size,
> + MSG_MORE);
> if (ret <= 0)
> goto out;
> con->v1.out_skip -= ret;
> diff --git a/net/ceph/messenger_v2.c b/net/ceph/messenger_v2.c
> index 87ac97073e75..139b61598f4f 100644
> --- a/net/ceph/messenger_v2.c
> +++ b/net/ceph/messenger_v2.c
> @@ -117,38 +117,89 @@ static int ceph_tcp_recv(struct ceph_connection *con)
> return ret;
> }
>
> +static int do_sendmsg(struct socket *sock, struct iov_iter *it)
> +{
> + struct msghdr msg = { .msg_flags = CEPH_MSG_FLAGS };
> + int ret;
> +
> + msg.msg_iter = *it;
> + while (iov_iter_count(it)) {
> + ret = sock_sendmsg(sock, &msg);
> + if (ret <= 0) {
> + if (ret == -EAGAIN)
> + ret = 0;
> + return ret;
> + }
> +
> + iov_iter_advance(it, ret);
> + }
> +
> + WARN_ON(msg_data_left(&msg));
> + return 1;
> +}
> +
> +static int do_try_sendpage(struct socket *sock, struct iov_iter *it)
> +{
> + struct msghdr msg = {};
> + struct bio_vec bv;
> + int ret;
> +
> + if (WARN_ON(!iov_iter_is_bvec(it)))
> + return -EINVAL;
> +
> + while (iov_iter_count(it)) {
> + msg.msg_flags = CEPH_MSG_FLAGS;
> + if (sendpage_ok(bv.bv_page))
> + msg.msg_flags |= MSG_SPLICE_PAGES;
> +
> + /* iov_iter_iovec() for ITER_BVEC */
> + bvec_set_page(&bv, it->bvec->bv_page,
> + min(iov_iter_count(it),
> + it->bvec->bv_len - it->iov_offset),
> + it->bvec->bv_offset + it->iov_offset);
> +
> + /*
> + * MSG_SPLICE_PAGES cannot properly handle pages with
> + * page_count == 0, we need to fall back to sendmsg if
> + * that's the case.
> + *
> + * Same goes for slab pages: skb_can_coalesce() allows
> + * coalescing neighboring slab objects into a single frag
> + * which triggers one of hardened usercopy checks.
> + */
This comment is now misplaced. I would suggest
if (sendpage_ok(bv.bv_page))
msg.msg_flags |= MSG_SPLICE_PAGES;
else
msg.msg_flags &= ~MSG_SPLICE_PAGES;
here and keeping the initialization
struct msghdr msg = { .msg_flags = CEPH_MSG_FLAGS };
above thus staying closer to the original.
Thanks,
Ilya
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