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RDMA/cm: Make it clearer how concurrency works in cm_req_handler()
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ib_crate_cm_id() immediately places the id in the xarray, and publishes it
into the remote_id and remote_qpn rbtrees. This makes it visible to other
threads before it is fully set up.

It appears the thinking here was that the states IB_CM_IDLE and
IB_CM_REQ_RCVD do not allow any MAD handler or lookup in the remote_id and
remote_qpn rbtrees to advance.

However, cm_rej_handler() does take an action on IB_CM_REQ_RCVD, which is
not really expected by the design.

Make the whole thing clearer:
 - Keep the new cm_id out of the xarray until it is completely set up.
   This directly prevents MAD handlers and all rbtree lookups from seeing
   the pointer.
 - Move all the trivial setup right to the top so it is obviously done
   before any concurrency begins
 - Move the mutation of the cm_id_priv out of cm_match_id() and into the
   caller so the state transition is obvious
 - Place the manipulation of the work_list at the end, under lock, after
   the cm_id is placed in the xarray. The work_count cannot change on an
   ID outside the xarray.
 - Add some comments

Link: https://lore.kernel.org/r/20200310092545.251365-9-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
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@jgunthorpe
jgunthorpe committed Mar 17, 2020
1 parent 083bfdb commit c206f8b
Showing 1 changed file with 57 additions and 42 deletions.
99 changes: 57 additions & 42 deletions drivers/infiniband/core/cm.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1958,14 +1958,10 @@ static struct cm_id_private * cm_match_req(struct cm_work *work,
cm_issue_rej(work->port, work->mad_recv_wc,
IB_CM_REJ_INVALID_SERVICE_ID, CM_MSG_RESPONSE_REQ,
NULL, 0);
goto out;
return NULL;
}
refcount_inc(&listen_cm_id_priv->refcount);
refcount_inc(&cm_id_priv->refcount);
cm_id_priv->id.state = IB_CM_REQ_RCVD;
atomic_inc(&cm_id_priv->work_count);
spin_unlock_irq(&cm.lock);
out:
return listen_cm_id_priv;
}

Expand Down Expand Up @@ -2007,7 +2003,6 @@ static void cm_process_routed_req(struct cm_req_msg *req_msg, struct ib_wc *wc)

static int cm_req_handler(struct cm_work *work)
{
struct ib_cm_id *cm_id;
struct cm_id_private *cm_id_priv, *listen_cm_id_priv;
struct cm_req_msg *req_msg;
const struct ib_global_route *grh;
Expand All @@ -2016,13 +2011,33 @@ static int cm_req_handler(struct cm_work *work)

req_msg = (struct cm_req_msg *)work->mad_recv_wc->recv_buf.mad;

cm_id = ib_create_cm_id(work->port->cm_dev->ib_device, NULL, NULL);
if (IS_ERR(cm_id))
return PTR_ERR(cm_id);
cm_id_priv =
cm_alloc_id_priv(work->port->cm_dev->ib_device, NULL, NULL);
if (IS_ERR(cm_id_priv))
return PTR_ERR(cm_id_priv);

cm_id_priv = container_of(cm_id, struct cm_id_private, id);
cm_id_priv->id.remote_id =
cpu_to_be32(IBA_GET(CM_REQ_LOCAL_COMM_ID, req_msg));
cm_id_priv->id.service_id =
cpu_to_be64(IBA_GET(CM_REQ_SERVICE_ID, req_msg));
cm_id_priv->id.service_mask = ~cpu_to_be64(0);
cm_id_priv->tid = req_msg->hdr.tid;
cm_id_priv->timeout_ms = cm_convert_to_ms(
IBA_GET(CM_REQ_LOCAL_CM_RESPONSE_TIMEOUT, req_msg));
cm_id_priv->max_cm_retries = IBA_GET(CM_REQ_MAX_CM_RETRIES, req_msg);
cm_id_priv->remote_qpn =
cpu_to_be32(IBA_GET(CM_REQ_LOCAL_QPN, req_msg));
cm_id_priv->initiator_depth =
IBA_GET(CM_REQ_RESPONDER_RESOURCES, req_msg);
cm_id_priv->responder_resources =
IBA_GET(CM_REQ_INITIATOR_DEPTH, req_msg);
cm_id_priv->path_mtu = IBA_GET(CM_REQ_PATH_PACKET_PAYLOAD_MTU, req_msg);
cm_id_priv->pkey = cpu_to_be16(IBA_GET(CM_REQ_PARTITION_KEY, req_msg));
cm_id_priv->sq_psn = cpu_to_be32(IBA_GET(CM_REQ_STARTING_PSN, req_msg));
cm_id_priv->retry_count = IBA_GET(CM_REQ_RETRY_COUNT, req_msg);
cm_id_priv->rnr_retry_count = IBA_GET(CM_REQ_RNR_RETRY_COUNT, req_msg);
cm_id_priv->qp_type = cm_req_get_qp_type(req_msg);

ret = cm_init_av_for_response(work->port, work->mad_recv_wc->wc,
work->mad_recv_wc->recv_buf.grh,
&cm_id_priv->av);
Expand All @@ -2034,27 +2049,26 @@ static int cm_req_handler(struct cm_work *work)
ret = PTR_ERR(cm_id_priv->timewait_info);
goto destroy;
}
cm_id_priv->timewait_info->work.remote_id =
cpu_to_be32(IBA_GET(CM_REQ_LOCAL_COMM_ID, req_msg));
cm_id_priv->timewait_info->work.remote_id = cm_id_priv->id.remote_id;
cm_id_priv->timewait_info->remote_ca_guid =
cpu_to_be64(IBA_GET(CM_REQ_LOCAL_CA_GUID, req_msg));
cm_id_priv->timewait_info->remote_qpn =
cpu_to_be32(IBA_GET(CM_REQ_LOCAL_QPN, req_msg));
cm_id_priv->timewait_info->remote_qpn = cm_id_priv->remote_qpn;

/*
* Note that the ID pointer is not in the xarray at this point,
* so this set is only visible to the local thread.
*/
cm_id_priv->id.state = IB_CM_REQ_RCVD;

listen_cm_id_priv = cm_match_req(work, cm_id_priv);
if (!listen_cm_id_priv) {
pr_debug("%s: local_id %d, no listen_cm_id_priv\n", __func__,
be32_to_cpu(cm_id->local_id));
be32_to_cpu(cm_id_priv->id.local_id));
cm_id_priv->id.state = IB_CM_IDLE;
ret = -EINVAL;
goto destroy;
}

cm_id_priv->id.cm_handler = listen_cm_id_priv->id.cm_handler;
cm_id_priv->id.context = listen_cm_id_priv->id.context;
cm_id_priv->id.service_id =
cpu_to_be64(IBA_GET(CM_REQ_SERVICE_ID, req_msg));
cm_id_priv->id.service_mask = ~cpu_to_be64(0);

cm_process_routed_req(req_msg, work->mad_recv_wc->wc);

memset(&work->path[0], 0, sizeof(work->path[0]));
Expand Down Expand Up @@ -2092,10 +2106,10 @@ static int cm_req_handler(struct cm_work *work)
work->port->port_num, 0,
&work->path[0].sgid);
if (err)
ib_send_cm_rej(cm_id, IB_CM_REJ_INVALID_GID,
ib_send_cm_rej(&cm_id_priv->id, IB_CM_REJ_INVALID_GID,
NULL, 0, NULL, 0);
else
ib_send_cm_rej(cm_id, IB_CM_REJ_INVALID_GID,
ib_send_cm_rej(&cm_id_priv->id, IB_CM_REJ_INVALID_GID,
&work->path[0].sgid,
sizeof(work->path[0].sgid),
NULL, 0);
Expand All @@ -2105,39 +2119,40 @@ static int cm_req_handler(struct cm_work *work)
ret = cm_init_av_by_path(&work->path[1], NULL,
&cm_id_priv->alt_av, cm_id_priv);
if (ret) {
ib_send_cm_rej(cm_id, IB_CM_REJ_INVALID_ALT_GID,
ib_send_cm_rej(&cm_id_priv->id,
IB_CM_REJ_INVALID_ALT_GID,
&work->path[0].sgid,
sizeof(work->path[0].sgid), NULL, 0);
goto rejected;
}
}
cm_id_priv->tid = req_msg->hdr.tid;
cm_id_priv->timeout_ms = cm_convert_to_ms(
IBA_GET(CM_REQ_LOCAL_CM_RESPONSE_TIMEOUT, req_msg));
cm_id_priv->max_cm_retries = IBA_GET(CM_REQ_MAX_CM_RETRIES, req_msg);
cm_id_priv->remote_qpn =
cpu_to_be32(IBA_GET(CM_REQ_LOCAL_QPN, req_msg));
cm_id_priv->initiator_depth =
IBA_GET(CM_REQ_RESPONDER_RESOURCES, req_msg);
cm_id_priv->responder_resources =
IBA_GET(CM_REQ_INITIATOR_DEPTH, req_msg);
cm_id_priv->path_mtu = IBA_GET(CM_REQ_PATH_PACKET_PAYLOAD_MTU, req_msg);
cm_id_priv->pkey = cpu_to_be16(IBA_GET(CM_REQ_PARTITION_KEY, req_msg));
cm_id_priv->sq_psn = cpu_to_be32(IBA_GET(CM_REQ_STARTING_PSN, req_msg));
cm_id_priv->retry_count = IBA_GET(CM_REQ_RETRY_COUNT, req_msg);
cm_id_priv->rnr_retry_count = IBA_GET(CM_REQ_RNR_RETRY_COUNT, req_msg);
cm_id_priv->qp_type = cm_req_get_qp_type(req_msg);

cm_id_priv->id.cm_handler = listen_cm_id_priv->id.cm_handler;
cm_id_priv->id.context = listen_cm_id_priv->id.context;
cm_format_req_event(work, cm_id_priv, &listen_cm_id_priv->id);

/* Now MAD handlers can see the new ID */
spin_lock_irq(&cm_id_priv->lock);
cm_finalize_id(cm_id_priv);

/* Refcount belongs to the event, pairs with cm_process_work() */
refcount_inc(&cm_id_priv->refcount);
atomic_inc(&cm_id_priv->work_count);
spin_unlock_irq(&cm_id_priv->lock);
cm_process_work(cm_id_priv, work);
/*
* Since this ID was just created and was not made visible to other MAD
* handlers until the cm_finalize_id() above we know that the
* cm_process_work() will deliver the event and the listen_cm_id
* embedded in the event can be derefed here.
*/
cm_deref_id(listen_cm_id_priv);
return 0;

rejected:
refcount_dec(&cm_id_priv->refcount);
cm_deref_id(listen_cm_id_priv);
destroy:
ib_destroy_cm_id(cm_id);
ib_destroy_cm_id(&cm_id_priv->id);
return ret;
}

Expand Down

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