From: Tiwei Bie <tiwei.bie@intel.com>
Date: Wed, 5 Sep 2018 04:28:50 +0000 (+0800)
Subject: net/virtio-user: fix deadlock in memory events callback
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=7ff269575bd144482d56a20fec61187f1af15dda;p=dpdk.git

net/virtio-user: fix deadlock in memory events callback

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>
Tested-by: Seán Harte <seanbh@gmail.com>
Reviewed-by: Seán Harte <seanbh@gmail.com>
Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---

diff --git a/drivers/net/virtio/virtio_user/vhost_kernel.c b/drivers/net/virtio/virtio_user/vhost_kernel.c
index d1be821626..a93fe5b289 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 7df600b02c..869e96f87e 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;
 }