From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Date: Mon, 27 Jan 2020 19:01:44 +0000

Subject: [PATCH] contrib/libvhost-user: Protect slave fd with mutex

MIME-Version: 1.0

Content-Type: text/plain; charset=UTF-8

Content-Transfer-Encoding: 8bit

In future patches we'll be performing commands on the slave-fd driven

by commands on queues, since those queues will be driven by individual

threads we need to make sure they don't attempt to use the slave-fd

for multiple commands in parallel.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

(cherry picked from commit c25c02b9e6a196be87a818f459c426556b24770d)

---

 contrib/libvhost-user/libvhost-user.c | 24 ++++++++++++++++++++----

 contrib/libvhost-user/libvhost-user.h |  3 +++

 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c

index ec27b78ff1..63e41062a4 100644

--- a/contrib/libvhost-user/libvhost-user.c

+++ b/contrib/libvhost-user/libvhost-user.c

@@ -392,26 +392,37 @@ vu_send_reply(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)

     return vu_message_write(dev, conn_fd, vmsg);

 }

+/*

+ * Processes a reply on the slave channel.

+ * Entered with slave_mutex held and releases it before exit.

+ * Returns true on success.

+ */

 static bool

 vu_process_message_reply(VuDev *dev, const VhostUserMsg *vmsg)

 {

     VhostUserMsg msg_reply;

+    bool result = false;

     if ((vmsg->flags & VHOST_USER_NEED_REPLY_MASK) == 0) {

-        return true;

+        result = true;

+        goto out;

     }

     if (!vu_message_read(dev, dev->slave_fd, &msg_reply)) {

-        return false;

+        goto out;

     }

     if (msg_reply.request != vmsg->request) {

         DPRINT("Received unexpected msg type. Expected %d received %d",

                vmsg->request, msg_reply.request);

-        return false;

+        goto out;

     }

-    return msg_reply.payload.u64 == 0;

+    result = msg_reply.payload.u64 == 0;

+

+out:

+    pthread_mutex_unlock(&dev->slave_mutex);

+    return result;

 }

 /* Kick the log_call_fd if required. */

@@ -1105,10 +1116,13 @@ bool vu_set_queue_host_notifier(VuDev *dev, VuVirtq *vq, int fd,

         return false;

     }

+    pthread_mutex_lock(&dev->slave_mutex);

     if (!vu_message_write(dev, dev->slave_fd, &vmsg)) {

+        pthread_mutex_unlock(&dev->slave_mutex);

         return false;

     }

+    /* Also unlocks the slave_mutex */

     return vu_process_message_reply(dev, &vmsg);

 }

@@ -1628,6 +1642,7 @@ vu_deinit(VuDev *dev)

         close(dev->slave_fd);

         dev->slave_fd = -1;

     }

+    pthread_mutex_destroy(&dev->slave_mutex);

     if (dev->sock != -1) {

         close(dev->sock);

@@ -1663,6 +1678,7 @@ vu_init(VuDev *dev,

     dev->remove_watch = remove_watch;

     dev->iface = iface;

     dev->log_call_fd = -1;

+    pthread_mutex_init(&dev->slave_mutex, NULL);

     dev->slave_fd = -1;

     dev->max_queues = max_queues;

diff --git a/contrib/libvhost-user/libvhost-user.h b/contrib/libvhost-user/libvhost-user.h

index 46b600799b..1844b6f8d4 100644

--- a/contrib/libvhost-user/libvhost-user.h

+++ b/contrib/libvhost-user/libvhost-user.h

@@ -19,6 +19,7 @@

 #include <stddef.h>

 #include <sys/poll.h>

 #include <linux/vhost.h>

+#include <pthread.h>

 #include "standard-headers/linux/virtio_ring.h"

 /* Based on qemu/hw/virtio/vhost-user.c */

@@ -355,6 +356,8 @@ struct VuDev {

     VuVirtq *vq;

     VuDevInflightInfo inflight_info;

     int log_call_fd;

+    /* Must be held while using slave_fd */

+    pthread_mutex_t slave_mutex;

     int slave_fd;

     uint64_t log_size;

     uint8_t *log_table;