On 02/28/13 22:27, Eric Blake wrote:
On 02/28/2013 08:25 AM, Michal Privoznik wrote:
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"));
s/mutext/mutex/
+ return -1;
+ }
+
+ retries = 20;
Do we really need to bump retries up, if the point of the mutex was to
prevent the need for that?
This will increase the chance we will succeed in a possible race with a
non-libvirt competitor, but it's not really needed for this fix.
On the other hand, as this fix is considered temporary and just done to
get the release out, I don't mind this change.
+ virMutexLock(&virNetDevMacVLanCreateMutex);
for (c = 0; c < 8192; c++) {
The loop here is anyways trying a lot of stuff for possible existing
interfaces so the bump of the retry count can't hurt performance really
much.
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;
+ }
Seems reasonable, but you might want a second reviewer since we are so
close to release.
The (temporary) fix seems okay to me. ACK if this gets cleaned up
properly after the release
Peter
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