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SUNRPC: Fix NFSD's request deferral on RDMA transports

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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 71641d99ce ("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>
This commit is contained in:
Chuck Lever 2022-04-01 17:08:21 -04:00
parent 999397926a
commit 773f91b2cf
3 changed files with 5 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/sunrpc/svc.h
View File

@ -395,6 +395,7 @@ 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;

3
net/sunrpc/svc_xprt.c
View File

@ -1231,6 +1231,8 @@ static struct cache_deferred_req *svc_defer(struct cache_req *req)
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;
@ -1269,6 +1271,7 @@ static noinline int svc_deferred_recv(struct svc_rqst *rqstp)
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;
}

2
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
View File

@ -831,7 +831,7 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
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;