Re: [libvirt] [PATCH] 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. --- @@ -870,23 +880,39 @@ int virNetDevMacVLanCreateWithVPortProfile(const char *tgifname, return -1; } else { create_name: - retries = 5; + if (virNetDevMacVLanCreateMutexInitialize() < 0) { + virReportSystemError(errno, "%s", _("unable to init mutext"));

+ return -1; + } + + retries = 20;

+ 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; + }