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NFSD: Force all NFSv4.2 COPY requests to be synchronous
We've discovered that delivering a CB_OFFLOAD operation can be unreliable in some pretty unremarkable situations. Examples include: - The server dropped the connection because it lost a forechannel NFSv4 request and wishes to force the client to retransmit - The GSS sequence number window under-flowed - A network partition occurred When that happens, all pending callback operations, including CB_OFFLOAD, are lost. NFSD does not retransmit them. Moreover, the Linux NFS client does not yet support sending an OFFLOAD_STATUS operation to probe whether an asynchronous COPY operation has finished. Thus, on Linux NFS clients, when a CB_OFFLOAD is lost, asynchronous COPY can hang until manually interrupted. I've tried a couple of remedies, but so far the side-effects are worse than the disease and they have had to be reverted. So temporarily force COPY operations to be synchronous so that the use of CB_OFFLOAD is avoided entirely. This is a fix that can easily be backported to LTS kernels. I am working on client patches that introduce an implementation of OFFLOAD_STATUS. Note that NFSD arbitrarily limits the size of a copy_file_range to 4MB to avoid indefinitely blocking an nfsd thread. A short COPY result is returned in that case, and the client can present a fresh COPY request for the remainder. Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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@ -1807,6 +1807,13 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
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__be32 status;
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struct nfsd4_copy *async_copy = NULL;
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/*
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* Currently, async COPY is not reliable. Force all COPY
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* requests to be synchronous to avoid client application
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* hangs waiting for COPY completion.
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*/
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nfsd4_copy_set_sync(copy, true);
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copy->cp_clp = cstate->clp;
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if (nfsd4_ssc_is_inter(copy)) {
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trace_nfsd_copy_inter(copy);
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