svcrdma: Tail iovec leaves an orphaned DMA mapping
commit cace564f upstream. The ctxt's count field is overloaded to mean the number of pages in the ctxt->page array and the number of SGEs in the ctxt->sge array. Typically these two numbers are the same. However, when an inline RPC reply is constructed from an xdr_buf with a tail iovec, the head and tail often occupy the same page, but each are DMA mapped independently. In that case, ->count equals the number of pages, but it does not equal the number of SGEs. There's one more SGE, for the tail iovec. Hence there is one more DMA mapping than there are pages in the ctxt->page array. This isn't a real problem until the server's iommu is enabled. Then each RPC reply that has content in that iovec orphans a DMA mapping that consists of real resources. krb5i and krb5p always populate that tail iovec. After a couple million sent krb5i/p RPC replies, the NFS server starts behaving erratically. Reboot is needed to clear the problem. Fixes: 9d11b51c ("svcrdma: Fix send_reply() scatter/gather set-up") Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com> [bwh: Backported to 3.16: - Adjust context - Drop changes to svc_rdma_bc_sendto() - s/xprt->sc_pd->local_dma_lkey/xprt->sc_dma_lkey/ Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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