[libvirt] [PATCH v2] virnetdevmacvlan.c: Introduce mutex for macvlan creation
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.
---
diff to v1:
-don't increase @retries
-move error reporting to virNetDevMacVLanCreateMutexOnceInit
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 a74db1e..ddea11f 100644
--- a/src/util/virnetdevmacvlan.c
+++ b/src/util/virnetdevmacvlan.c
@@ -31,6 +31,7 @@
#include "virmacaddr.h"
#include "virutil.h"
#include "virerror.h"
+#include "virthread.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:
*
@@ -829,7 +843,7 @@ 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;
@@ -871,22 +885,35 @@ 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,
--
1.8.1.4