File libvirt-virnetdevmacvlan.c-Introduce-mutex-for-macvlan-creation.patch of Package libvirt

From 01ac8f1b000a6c850e552f4d0c4128db5378c2fb Mon Sep 17 00:00:00 2001
Message-Id: <01ac8f1b000a6c850e552f4d0c4128db5378c2fb@dist-git>
From: Michal Privoznik <mprivozn@redhat.com>
Date: Mon, 15 Feb 2016 06:59:46 -0500
Subject: [PATCH] virnetdevmacvlan.c: Introduce mutex for macvlan creation

Part of fix for: https://bugzilla.redhat.com/show_bug.cgi?id=1276478

Currently, after we removed the qemu driver lock, it may happen
that two or more threads will start up a machine with macvlan and
race over virNetDevMacVLanCreateWithVPortProfile(). However,
there's a racy section in which we are generating a sequence of
possible device names and detecting if they exits. If we found
one which doesn't we try to create a device with that name.
However, the other thread is doing just the same. Assume it will
succeed and we must therefore fail. If this happens more than 5
times (which in massive parallel startup surely will) we return
-1 without any error reported. This patch is a simple hack to
both of these problems. It introduces a mutex, so only one thread
will enter the section, and if it runs out of possibilities,
error is reported. Moreover, the number of retries is raised to 20.

(cherry picked from commit 1cf97c87c05bc44d577d545d29d9c94764ea5975
with minor merge conflict due to header renaming upstream)

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
---
 src/util/virnetdevmacvlan.c | 37 ++++++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/src/util/virnetdevmacvlan.c b/src/util/virnetdevmacvlan.c
index 0795c23..4a6cb69 100644
--- a/src/util/virnetdevmacvlan.c
+++ b/src/util/virnetdevmacvlan.c
@@ -31,6 +31,7 @@
 #include "virmacaddr.h"
 #include "util.h"
 #include "virterror_internal.h"
+#include "threads.h"
 
 #define VIR_FROM_THIS VIR_FROM_NET
 
@@ -71,6 +72,19 @@ VIR_ENUM_IMPL(virNetDevMacVLanMode, VIR_NETDEV_MACVLAN_MODE_LAST,
 # define MACVLAN_NAME_PREFIX	"macvlan"
 # define MACVLAN_NAME_PATTERN	"macvlan%d"
 
+virMutex virNetDevMacVLanCreateMutex;
+
+static int virNetDevMacVLanCreateMutexOnceInit(void)
+{
+    if (virMutexInit(&virNetDevMacVLanCreateMutex) < 0) {
+        virReportSystemError(errno, "%s", _("unable to init mutex"));
+        return -1;
+    }
+    return 0;
+}
+
+VIR_ONCE_GLOBAL_INIT(virNetDevMacVLanCreateMutex);
+
 /**
  * virNetDevMacVLanCreate:
  *
@@ -836,7 +850,7 @@ int virNetDevMacVLanCreateWithVPortProfile(const char *tgifname,
     char ifname[IFNAMSIZ];
     int retries, do_retry = 0;
     uint32_t macvtapMode;
-    const char *cr_ifname;
+    const char *cr_ifname = NULL;
     int ret;
     int vf = -1;
 
@@ -902,22 +916,35 @@ int virNetDevMacVLanCreateWithVPortProfile(const char *tgifname,
     } else {
 create_name:
         retries = 5;
+        if (virNetDevMacVLanCreateMutexInitialize() < 0)
+            return -1;
+        virMutexLock(&virNetDevMacVLanCreateMutex);
         for (c = 0; c < 8192; c++) {
             snprintf(ifname, sizeof(ifname), pattern, c);
-            if ((ret = virNetDevExists(ifname)) < 0)
+            if ((ret = virNetDevExists(ifname)) < 0) {
+                virMutexUnlock(&virNetDevMacVLanCreateMutex);
                 return -1;
+            }
             if (!ret) {
                 rc = virNetDevMacVLanCreate(ifname, type, macaddress, linkdev,
                                             macvtapMode, &do_retry);
-                if (rc == 0)
+                if (rc == 0) {
+                    cr_ifname = ifname;
                     break;
+                }
 
                 if (do_retry && --retries)
                     continue;
-                return -1;
+                break;
             }
         }
-        cr_ifname = ifname;
+
+        virMutexUnlock(&virNetDevMacVLanCreateMutex);
+        if (!cr_ifname) {
+            virReportError(VIR_ERR_OPERATION_FAILED, "%s",
+                           _("Unable to create macvlan device"));
+            return -1;
+        }
     }
 
     if (virNetDevVPortProfileAssociate(cr_ifname,
-- 
2.7.1