> On Dec 9, 2020, at 11:47 AM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>
> 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.
Excellent, thanks for confirming!
>> 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);
--
Chuck Lever
