[dpdk-dev] [PATCH 3/3] eal: handle bus rescan failures during hotplug

[Darek Stojaczyk <dariusz.stojaczyk@intel.com>]

Fixes for devargs dangling pointers and various segfaults
caused by failed hotplug requests.

If rescan failed, we have one the following scenarios
to cover:
 a) the device was never scanned at all; the devargs that
    were just allocated are not referenced anywhere and
    can be removed straight away. Previous devargs (if any)
    need to be re-inserted as they are still in use.
 b) the device was scanned before, but the rescan failed
    before it reached our device, meaning that its devargs
    were not overridden and we can remove our newly allocated
    ones. Previous devargs need to be re-inserted.
 c) we managed to rescan our device and only failed on
    something after that, which means we have to free the
    memory of previous devargs and stick with the new ones,
    despite the fact that the hotplug still needs to be
    failed.

Fixes: 7e8b26650146 ("eal: fix hotplug add / remove")
Cc: gaetan.rivet@6wind.com
Cc: qi.z.zhang@intel.com

Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
---
 lib/librte_eal/common/eal_common_dev.c | 30 ++++++++++++++++++--------
 1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_dev.c b/lib/librte_eal/common/eal_common_dev.c
index 4cb424df1..b090295b9 100644
--- a/lib/librte_eal/common/eal_common_dev.c
+++ b/lib/librte_eal/common/eal_common_dev.c
@@ -7,6 +7,7 @@
 #include <string.h>
 #include <inttypes.h>
 #include <sys/queue.h>
+#include <assert.h>
 
 #include <rte_compat.h>
 #include <rte_bus.h>
@@ -141,32 +142,33 @@ local_dev_probe(const char *devargs, struct rte_device **new_dev)
 
 	ret = rte_devargs_parse(da, devargs);
 	if (ret)
-		goto err_devarg;
+		goto err_remove_devargs;
 
 	if (da->bus->plug == NULL) {
 		RTE_LOG(ERR, EAL, "Function plug not supported by bus (%s)\n",
 			da->bus->name);
 		ret = -ENOTSUP;
-		goto err_devarg;
+		goto err_remove_devargs;
 	}
 
 	rte_devargs_insert(da, &prev_da);
 
+	ret = da->bus->scan();
+	if (ret)
+		goto err_rollback_devargs;
+
 	if (prev_da != NULL) {
 		free(prev_da->args);
 		free(prev_da);
+		prev_da = NULL;
 	}
 
-	ret = da->bus->scan();
-	if (ret)
-		goto err_devarg;
-
 	dev = da->bus->find_device(NULL, cmp_dev_name, da->name);
 	if (dev == NULL) {
 		RTE_LOG(ERR, EAL, "Cannot find device (%s)\n",
 			da->name);
 		ret = -ENODEV;
-		goto err_devarg;
+		goto err_remove_devargs;
 	}
 
 	ret = dev->bus->plug(dev);
@@ -175,13 +177,23 @@ local_dev_probe(const char *devargs, struct rte_device **new_dev)
 			return ret; /* no rollback */
 		RTE_LOG(ERR, EAL, "Driver cannot attach the device (%s)\n",
 			dev->name);
-		goto err_devarg;
+		goto err_remove_devargs;
 	}
 
 	*new_dev = dev;
 	return 0;
 
-err_devarg:
+err_rollback_devargs:
+	dev = da->bus->find_device(NULL, cmp_dev_name, da->name);
+	if (prev_da != NULL && (dev == NULL || dev->devargs != da)) {
+		/* either the device wasn't scanned, or we didn't
+		 * manage yet to update its devargs.
+		 */
+		rte_devargs_insert(prev_da, &da);
+		assert(da != NULL);
+	}
+
+err_remove_devargs:
 	if (rte_devargs_remove(da) != 0) {
 		free(da->args);
 		free(da);
-- 
2.17.1