[PATCH 1/3] net/virtio-user: fix deadlock in memory events callback

[Tiwei Bie <tiwei.bie@intel.com>]

Deadlock can occur when allocating memory if a vhost-kernel
based virtio-user device is in use. To fix the deadlock,
we will take memory hotplug lock explicitly in virtio-user
when necessary, and always call the _thread_unsafe memory
functions.

Bugzilla ID: 81
Fixes: 12ecb2f63b12 ("net/virtio-user: support memory hotplug")
Cc: stable@dpdk.org

Reported-by: Seán Harte <seanbh@gmail.com>
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
---
 drivers/net/virtio/virtio_user/vhost_kernel.c |  6 +++++-
 .../net/virtio/virtio_user/virtio_user_dev.c  | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio/virtio_user/vhost_kernel.c b/drivers/net/virtio/virtio_user/vhost_kernel.c
index b2444096c..897fee0af 100644
--- a/drivers/net/virtio/virtio_user/vhost_kernel.c
+++ b/drivers/net/virtio/virtio_user/vhost_kernel.c
@@ -115,7 +115,11 @@ prepare_vhost_memory_kernel(void)
 	wa.region_nr = 0;
 	wa.vm = vm;
 
-	if (rte_memseg_contig_walk(add_memory_region, &wa) < 0) {
+	/*
+	 * The memory lock has already been taken by memory subsystem
+	 * or virtio_user_start_device().
+	 */
+	if (rte_memseg_contig_walk_thread_unsafe(add_memory_region, &wa) < 0) {
 		free(vm);
 		return NULL;
 	}
diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c b/drivers/net/virtio/virtio_user/virtio_user_dev.c
index 7df600b02..869e96f87 100644
--- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
+++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c
@@ -13,6 +13,8 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
+#include <rte_eal_memconfig.h>
+
 #include "vhost.h"
 #include "virtio_user_dev.h"
 #include "../virtio_ethdev.h"
@@ -109,9 +111,24 @@ is_vhost_user_by_type(const char *path)
 int
 virtio_user_start_device(struct virtio_user_dev *dev)
 {
+	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
 	uint64_t features;
 	int ret;
 
+	/*
+	 * XXX workaround!
+	 *
+	 * We need to make sure that the locks will be
+	 * taken in the correct order to avoid deadlocks.
+	 *
+	 * Before releasing this lock, this thread should
+	 * not trigger any memory hotplug events.
+	 *
+	 * This is a temporary workaround, and should be
+	 * replaced when we get proper supports from the
+	 * memory subsystem in the future.
+	 */
+	rte_rwlock_read_lock(&mcfg->memory_hotplug_lock);
 	pthread_mutex_lock(&dev->mutex);
 
 	if (is_vhost_user_by_type(dev->path) && dev->vhostfd < 0)
@@ -152,10 +169,12 @@ virtio_user_start_device(struct virtio_user_dev *dev)
 
 	dev->started = true;
 	pthread_mutex_unlock(&dev->mutex);
+	rte_rwlock_read_unlock(&mcfg->memory_hotplug_lock);
 
 	return 0;
 error:
 	pthread_mutex_unlock(&dev->mutex);
+	rte_rwlock_read_unlock(&mcfg->memory_hotplug_lock);
 	/* TODO: free resource here or caller to check */
 	return -1;
 }
-- 
2.18.0