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Re: [libvirt] [PATCH] do not unref obj in qemuDomainObjExitMonitorWithDriver



On 03/17/2011 10:25 PM, Wen Congyang wrote:
At 03/17/2011 07:11 PM, Daniel P. Berrange Write:
On Wed, Mar 16, 2011 at 05:01:23PM +0800, Wen Congyang wrote:
Steps to reproduce this bug:
# cat test.sh
   #! /bin/bash -x
   virsh start domain
   sleep 5
   virsh qemu-monitor-command domain 'cpu_set 2 online' --hmp
# while true; do ./test.sh ; done

Then libvirtd will crash.

The reason is that:
we add a reference of obj when we open the monitor. We will reduce this
reference when we free the monitor.

If the reference of monitor is 0, we will free monitor automatically and
the reference of obj is reduced.

But in the function qemuDomainObjExitMonitorWithDriver(), we reduce this
reference again when the reference of monitor is 0.

It will cause the obj be freed in the function qemuDomainObjEndJob().

Then we start the domain again, and libvirtd will crash in the function
virDomainObjListSearchName(), because we pass a null pointer(obj->def->name)
to strcmp().

Signed-off-by: Wen Congyang<wency cn fujitsu com>

---
  src/qemu/qemu_domain.c |    1 -
  1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 8a2b9cc..ae28b1c 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -634,7 +634,6 @@ void qemuDomainObjExitMonitorWithDriver(struct qemud_driver *driver,
      virDomainObjLock(obj);

      if (refs == 0) {
-        virDomainObjUnref(obj);
          priv->mon = NULL;
      }
  }
ACK,  ExitMonitorWithDriver should not be touching the virDomainObjPtr
refs at all. The virDomainObjPtr refs should only be touched by the
BeginJob/EndJob calls.

This same fix also needs to be done in qemuDomainObjExitMonitor()
Yes, there is the same problem in qemuDomainObjExitMonitor().
I have updated this patch.


ACK to this V2 (partially based on Dan's approval). I just pushed it.



Daniel

> From 6c30534f7e6c5d2e5661c38397fc5062a8288ef3 Mon Sep 17 00:00:00 2001
From: Wen Congyang<wency cn fujitsu com>
Date: Fri, 18 Mar 2011 09:51:07 +0800
Subject: [PATCH 3/3] do not unref obj in qemuDomainObjExitMonitor*

---
  src/qemu/qemu_domain.c |    2 --
  1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 8a2b9cc..cc137d2 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -588,7 +588,6 @@ void qemuDomainObjExitMonitor(virDomainObjPtr obj)
      virDomainObjLock(obj);

      if (refs == 0) {
-        virDomainObjUnref(obj);
          priv->mon = NULL;
      }
  }
@@ -634,7 +633,6 @@ void qemuDomainObjExitMonitorWithDriver(struct qemud_driver *driver,
      virDomainObjLock(obj);

      if (refs == 0) {
-        virDomainObjUnref(obj);
          priv->mon = NULL;
      }
  }


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