On Tue, Dec 8, 2020 at 6:31 PM Chuck Lever <chuck.lever@xxxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---
> 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);
>
>
