[dpdk-dev] [PATCH] dev: fix attach rollback of a device that was already attached

[Darek Stojaczyk]

When primary process receives an IPC attach request
of a device that's already locally-attached, it
doesn't setup its variables properly and is prone to
segfaulting on a subsequent rollback.

`ret = local_dev_probe(req->devargs, &dev)`

The above function will set `dev` pointer to the
proper device *unless* it returns with error. One of
those errors is -EEXIST, which the hotplug function
explicitly ignores. For -EEXIST, it proceeds with
attaching the device and expects the dev pointer to
be valid.

Despite this patch being a fix, it also introduces
a design decision - when any secondary process fails
to attach a device, the primary process that already
had the device attached won't attempt to detach that
device locally as a part of the rollback routine.
Primary process would have already printed a message
"Failed to [...] on secondary" and now it will also
print a warning "Devices may not be in sync [...]".

Fixes: ac9e4a17370f ("eal: support attach/detach shared device from secondary")
Cc: qi.z.zhang at intel.com

Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk at intel.com>
---
 lib/librte_eal/common/hotplug_mp.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/librte_eal/common/hotplug_mp.c b/lib/librte_eal/common/hotplug_mp.c
index 7c9fcc46c..7ee074a31 100644
--- a/lib/librte_eal/common/hotplug_mp.c
+++ b/lib/librte_eal/common/hotplug_mp.c
@@ -88,7 +88,7 @@ __handle_secondary_request(void *param)
 		(const struct eal_dev_mp_req *)msg->param;
 	struct eal_dev_mp_req tmp_req;
 	struct rte_devargs *da;
-	struct rte_device *dev;
+	struct rte_device *dev = NULL;
 	struct rte_bus *bus;
 	int ret = 0;
 
@@ -168,7 +168,15 @@ __handle_secondary_request(void *param)
 	if (req->t == EAL_DEV_REQ_TYPE_ATTACH) {
 		tmp_req.t = EAL_DEV_REQ_TYPE_ATTACH_ROLLBACK;
 		eal_dev_hotplug_request_to_secondary(&tmp_req);
-		local_dev_remove(dev);
+		if (dev == NULL) {
+			/* device was already attached at the time we got the
+			 * request, don't detach it now.
+			 */
+			RTE_LOG(WARNING, EAL,
+				"Devices in secondary may not sync with primary\n");
+		} else {
+			local_dev_remove(dev);
+		}
 	} else {
 		tmp_req.t = EAL_DEV_REQ_TYPE_DETACH_ROLLBACK;
 		eal_dev_hotplug_request_to_secondary(&tmp_req);
-- 
2.17.1