Re: [libvirt] [PATCH v2] nwfilter: fix deadlock when nwfilter reload
On 09/13/2018 07:15 AM, Wang Yechao wrote:
user run "firewalld-cmd --reload"
nwfilterStateReload called in main thread
step 1. virRWLockWrite(&updateLock)
step 2. virNWFilterLoadAllConfigs
step 3. virRWLockUnlock(&updateLock);
lauch a vm: qemuDomainCreateXML runs in other thread
step 1. virRWLockRead(&updateLock);
step 2. qemuProcessStart
step 3. qemuProcessWaitForMonitor
step 4. ...
step 5 virRWLockUnlock(&updateLock);
if nwfilterStateReload called in the middle of step 1 and step 5 of
qemuDomainCreateXML, it can't get the updateLock and then block the event_loop,
so event_loop can't handle the qemu-monitor messages, cause deadlock
move nwfilterStateReload into thread to fix this problem.
Signed-off-by: Wang Yechao <wang.yechao255(a)zte.com.cn>
Reviewed-by: Wang Yi <wang.yi59(a)zte.com.cn>
---
src/nwfilter/nwfilter_driver.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
Couple of "administrative" comments - since you were a new contributor
to libvir-list - you just needed to be a bit more patient w/r/t getting
your patches on this list, as described here:
https://libvirt.org/hacking.html
"If everything went well, your patch should show up on the libvir-list
archives in a matter of minutes; if you still can't find it on there
after an hour or so, you should double-check your setup. Note that your
very first post to the mailing list will be subject to moderation, and
it's not uncommon for that to take around a day.
"
OK so that hopefully helps explain why there were many v1's posted
Then when you repost a few days later with something that's changed, you
need to change to using v2. In the postings on Sept 11 it seems you've
change the R-By email address. That's important enough to note...
Then when you posted as v2, it probably should have been v3 and a note
added why you changed from VIR_ERROR to VIR_WARN
For each of these addition versions after the "---" (above):
1. Add a pointer to the previous posting from the archives
2. Briefly describe the differences in the changes
So, after all that... This seemed really familiar... and it was:
See:
https://www.redhat.com/archives/libvir-list/2017-October/msg01351.html
and follow-ups:
https://www.redhat.com/archives/libvir-list/2017-December/msg00198.html
https://www.redhat.com/archives/libvir-list/2017-December/msg00227.html
However, that followup was essentially dropped. So this code once again
resurrects the same questions that I had back then.
Not that I don't think this should be done in some form, the question
becomes how much "care" needs to be taken to ensure we don't have
multiple threads running.
John
BTW: Whether you were aware of Nikolay's patch or not, I think some
attribution could be made even though it was the same solution.
diff --git a/src/nwfilter/nwfilter_driver.c
b/src/nwfilter/nwfilter_driver.c
index 1ee5162..ab85072 100644
--- a/src/nwfilter/nwfilter_driver.c
+++ b/src/nwfilter/nwfilter_driver.c
@@ -80,18 +80,26 @@ static void nwfilterDriverUnlock(void)
}
#if HAVE_FIREWALLD
+static void nwfilterReloadThread(void *opaque ATTRIBUTE_UNUSED)
+{
+ nwfilterStateReload();
+}
static DBusHandlerResult
nwfilterFirewalldDBusFilter(DBusConnection *connection ATTRIBUTE_UNUSED,
DBusMessage *message,
void *user_data ATTRIBUTE_UNUSED)
{
+ virThread thread;
+
if (dbus_message_is_signal(message, DBUS_INTERFACE_DBUS,
"NameOwnerChanged") ||
dbus_message_is_signal(message, "org.fedoraproject.FirewallD1",
"Reloaded")) {
VIR_DEBUG("Reload in nwfilter_driver because of firewalld.");
- nwfilterStateReload();
+
+ if (virThreadCreate(&thread, false, nwfilterReloadThread, NULL) < 0)
+ VIR_WARN("create nwfilterReloadThread failed.");
}
return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;