[PATCH 5.17 184/219] SUNRPC: Fix NFSDs request deferral on RDMA transports

Greg Kroah-Hartman
2022-04-18T12:37:20Z

From: Chuck Lever <chuck.lever@oracle.com>

commit 773f91b2cf3f52df0d7508fdbf60f37567cdaee4 upstream.

Trond Myklebust reports an NFSD crash in svc_rdma_sendto(). Further
investigation shows that the crash occurred while NFSD was handling
a deferred request.

This patch addresses two inter-related issues that prevent request
deferral from working correctly for RPC/RDMA requests:

1. Prevent the crash by ensuring that the original
svc_rqst::rq_xprt_ctxt value is available when the request is
revisited. Otherwise svc_rdma_sendto() does not have a Receive
context available with which to construct its reply.

2. Possibly since before commit 71641d99ce03 ("svcrdma: Properly
compute .len and .buflen for received RPC Calls"),
svc_rdma_recvfrom() did not include the transport header in the
returned xdr_buf. There should have been no need for svc_defer()
and friends to save and restore that header, as of that commit.
This issue is addressed in a backport-friendly way by simply
having svc_rdma_recvfrom() set rq_xprt_hlen to zero
unconditionally, just as svc_tcp_recvfrom() does. This enables
svc_deferred_recv() to correctly reconstruct an RPC message
received via RPC/RDMA.

Reported-by: Trond Myklebust <trondmy@hammerspace.com>
Link: https://lore.kernel.org/linux-nfs/82662b7190f26fb304eb0ab1bb04279072439d4e.camel@hammerspace.com/
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/sunrpc/svc.h | 1 +
net/sunrpc/svc_xprt.c | 3 +++
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 2 +-
3 files changed, 5 insertions(+), 1 deletion(-)

--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -412,6 +412,7 @@ struct svc_deferred_req {
size_t addrlen;
struct sockaddr_storage daddr; /* where reply must come from */
size_t daddrlen;
+ void *xprt_ctxt;
struct cache_deferred_req handle;
size_t xprt_hlen;
int argslen;
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1213,6 +1213,8 @@ static struct cache_deferred_req *svc_de
dr->daddr = rqstp->rq_daddr;
dr->argslen = rqstp->rq_arg.len >> 2;
dr->xprt_hlen = rqstp->rq_xprt_hlen;
+ dr->xprt_ctxt = rqstp->rq_xprt_ctxt;
+ rqstp->rq_xprt_ctxt = NULL;

/* back up head to the start of the buffer and copy */
skip = rqstp->rq_arg.len - rqstp->rq_arg.head[0].iov_len;
@@ -1251,6 +1253,7 @@ static noinline int svc_deferred_recv(st
rqstp->rq_xprt_hlen = dr->xprt_hlen;
rqstp->rq_daddr = dr->daddr;
rqstp->rq_respages = rqstp->rq_pages;
+ rqstp->rq_xprt_ctxt = dr->xprt_ctxt;
svc_xprt_received(rqstp->rq_xprt);
return (dr->argslen<<2) - dr->xprt_hlen;
}
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -831,7 +831,7 @@ int svc_rdma_recvfrom(struct svc_rqst *r
goto out_err;
if (ret == 0)
goto out_drop;
- rqstp->rq_xprt_hlen = ret;
+ rqstp->rq_xprt_hlen = 0;

if (svc_rdma_is_reverse_direction_reply(xprt, ctxt))
goto out_backchannel;