> -----Original Message----- > From: Chuck Lever [mailto:chuck.lever@xxxxxxxxxx] > Sent: Monday, July 21, 2014 9:54 AM > To: Devesh Sharma > Cc: Shirley Ma; Steve Wise; Hefty, Sean; Roland Dreier; linux-rdma@xxxxxxxxxxxxxxx > Subject: Re: [for-next 1/2] xprtrdma: take reference of rdma provider module > > Hi Devesh- > > Thanks for drilling into this further. > > On Jul 21, 2014, at 7:48 AM, Devesh Sharma <Devesh.Sharma@xxxxxxxxxx> wrote: > > > In rpcrdma_ep_connect(): > > > > write_lock(&ia->ri_qplock); > > old = ia->ri_id; > > ia->ri_id = id; > > write_unlock(&ia->ri_qplock); > > > > rdma_destroy_qp(old); > > rdma_destroy_id(old); =============> Cm -id is destroyed here. > > > > > > If following code fails in rpcrdma_ep_connect(): > > id = rpcrdma_create_id(xprt, ia, > > (struct sockaddr *)&xprt->rx_data.addr); > > if (IS_ERR(id)) { > > rc = -EHOSTUNREACH; > > goto out; > > } > > > > it leaves old cm-id still alive. This will always fail if Device is removed abruptly. > > For CM_EVENT_DEVICE_REMOVAL, rpcrdma_conn_upcall() sets ep->rep_connected > to -ENODEV. > > Then: > > 929 int > 930 rpcrdma_ep_connect(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia) > 931 { > 932 struct rdma_cm_id *id, *old; > 933 int rc = 0; > 934 int retry_count = 0; > 935 > 936 if (ep->rep_connected != 0) { > 937 struct rpcrdma_xprt *xprt; > 938 retry: > 939 dprintk("RPC: %s: reconnecting...\n", __func__); > > ep->rep_connected is probably -ENODEV after a device removal. It would be > possible for the connect worker to destroy everything associated with this > connection in that case to ensure the underlying object reference counts > are cleared. > > The immediate danger is that if there are pending RPCs, they could exit while > qp/cm_id are NULL, triggering a panic in rpcrdma_deregister_frmr_external(). > Checking for NULL pointers inside the ri_qplock would prevent that. > > However, NFS mounts via this adapter will hang indefinitely after all > transports are torn down and the adapter is gone. The only thing that can be > done is something drastic like "echo b > /proc/sysrq_trigger" on the client. > > Thus, IMO hot-plugging or passive fail-over are the only scenarios where > this makes sense. If we have an immediate problem here, is it a problem with > system shutdown ordering that can be addressed in some other way? > > Until that support is in place, obviously I would prefer that the removal of > the underlying driver be prevented while there are NFS mounts in place. I > think that's what NFS users have come to expect. > > In other words, don't allow device removal until we have support for device > insertion :-) > > If we fix the above problems on provider unload, shouldn't the mount recover if the provider module is subsequently loaded? Or another provider configured such that rdma_resolve_addr/route() then picks an active device? -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
