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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Wed, 9 Dec 2020 11:47:26 -0500
Message-ID: <CAN-5tyGPzJUSSb3SGixo0L+CcFV=A12Er5+R=egc3orA9rz8Aw@mail.gmail.com>
Subject: Re: [PATCH v5] xprtrdma: Fix XDRBUF_SPARSE_PAGES support
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     linux-nfs <linux-nfs@vger.kernel.org>
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On Tue, Dec 8, 2020 at 6:31 PM Chuck Lever <chuck.lever@oracle.com> wrote:
>
> Olga K. observed that rpcrdma_marsh_req() allocates sparse pages
> only when it has determined that a Reply chunk is necessary. There
> are plenty of cases where no Reply chunk is needed, but the
> XDRBUF_SPARSE_PAGES flag is set. The result would be a crash in
> rpcrdma_inline_fixup() when it tries to copy parts of the received
> Reply into a missing page.
>
> To avoid crashing, handle sparse page allocation up front.
>
> Until XATTR support was added, this issue did not appear often
> because the only SPARSE_PAGES consumer always expected a reply large
> enough to always require a Reply chunk.
>
> Reported-by: Olga Kornievskaia <kolga@netapp.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> Cc: <stable@vger.kernel.org>
> ---
>  net/sunrpc/xprtrdma/rpc_rdma.c |   40 +++++++++++++++++++++++++++++++---------
>  1 file changed, 31 insertions(+), 9 deletions(-)
>
> Hi-
>
> v4 had a bug, which I've fixed. This version has been tested.

This version on top of the same commit  (rc4) passes generic/013
without oopsing for me too.

> In kernels before 5.10-rc5, there are still problems with the way
> LISTXATTRS and GETXATTR deal with the tail / XDR pad for the page
> content that this patch does not address. So backporting this fix
> alone is not enough to get those working again -- more surgery would
> be required.
>
> Since none of the other SPARSE_PAGES users have a problem, let's
> leave this one on the cutting room floor. It's here in the mail
> archive if anyone needs it.
>
>
> Changes since v4:
> - xdr_buf_pagecount() was simply the wrong thing to use.
>
> Changes since v3:
> - I swear I am not drunk. I forgot to commit the change before mailing it.
>
> Changes since v2:
> - Actually fix the xdr_buf_pagecount() problem
>
> Changes since RFC:
> - Ensure xdr_buf_pagecount() is defined in rpc_rdma.c
> - noinline the sparse page allocator -- it's an uncommon path
>
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index 0f5120c7668f..c48536f2121f 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -179,6 +179,31 @@ rpcrdma_nonpayload_inline(const struct rpcrdma_xprt *r_xprt,
>                 r_xprt->rx_ep->re_max_inline_recv;
>  }
>
> +/* ACL likes to be lazy in allocating pages. For TCP, these
> + * pages can be allocated during receive processing. Not true
> + * for RDMA, which must always provision receive buffers
> + * up front.
> + */
> +static noinline int
> +rpcrdma_alloc_sparse_pages(struct xdr_buf *buf)
> +{
> +       struct page **ppages;
> +       int len;
> +
> +       len = buf->page_len;
> +       ppages = buf->pages + (buf->page_base >> PAGE_SHIFT);
> +       while (len > 0) {
> +               if (!*ppages)
> +                       *ppages = alloc_page(GFP_NOWAIT | __GFP_NOWARN);
> +               if (!*ppages)
> +                       return -ENOBUFS;
> +               ppages++;
> +               len -= PAGE_SIZE;
> +       }
> +
> +       return 0;
> +}
> +
>  /* Split @vec on page boundaries into SGEs. FMR registers pages, not
>   * a byte range. Other modes coalesce these SGEs into a single MR
>   * when they can.
> @@ -233,15 +258,6 @@ rpcrdma_convert_iovs(struct rpcrdma_xprt *r_xprt, struct xdr_buf *xdrbuf,
>         ppages = xdrbuf->pages + (xdrbuf->page_base >> PAGE_SHIFT);
>         page_base = offset_in_page(xdrbuf->page_base);
>         while (len) {
> -               /* ACL likes to be lazy in allocating pages - ACLs
> -                * are small by default but can get huge.
> -                */
> -               if (unlikely(xdrbuf->flags & XDRBUF_SPARSE_PAGES)) {
> -                       if (!*ppages)
> -                               *ppages = alloc_page(GFP_NOWAIT | __GFP_NOWARN);
> -                       if (!*ppages)
> -                               return -ENOBUFS;
> -               }
>                 seg->mr_page = *ppages;
>                 seg->mr_offset = (char *)page_base;
>                 seg->mr_len = min_t(u32, PAGE_SIZE - page_base, len);
> @@ -867,6 +883,12 @@ rpcrdma_marshal_req(struct rpcrdma_xprt *r_xprt, struct rpc_rqst *rqst)
>         __be32 *p;
>         int ret;
>
> +       if (unlikely(rqst->rq_rcv_buf.flags & XDRBUF_SPARSE_PAGES)) {
> +               ret = rpcrdma_alloc_sparse_pages(&rqst->rq_rcv_buf);
> +               if (ret)
> +                       return ret;
> +       }
> +
>         rpcrdma_set_xdrlen(&req->rl_hdrbuf, 0);
>         xdr_init_encode(xdr, &req->rl_hdrbuf, rdmab_data(req->rl_rdmabuf),
>                         rqst);
>
>