Re: [libvirt] [PATCH 3/6] use virObject to manage reference-count of virDomainObj

On Tue, Apr 12, 2011 at 06:22:12PM +0800, Wen Congyang wrote: > At 04/12/2011 01:51 PM, Hu Tao Write: > > Sorry, I unexpectedly deleted text body. > > > > I changed the code like this: > > > > diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c > > index c2a1f9a..8aad0b3 100644 > > --- a/src/qemu/qemu_domain.c > > +++ b/src/qemu/qemu_domain.c > > @@ -514,7 +514,10 @@ int qemuDomainObjBeginJobWithDriver(struct qemud_driver *driver, > > else > > virReportSystemError(errno, > > "%s", _("cannot acquire job mutex")); > > + virDomainObjUnlock(obj); > > qemuDriverLock(driver); > > + virDomainObjLock(obj); > > We lock qemu_driver and vm as the folling steps: > 1. lock qemu_driver > 2. lock vm > > We try to lock qemu_driver while holding the vm's lock. > OOps, it will cause the libvirtd deadlock.(I can reproduce this bug by your script) > > > + virDomainObjUnref(obj); > > We have unref it, so do not unref it again. Didn't see there is already a call to virDomainObjUnref. the patch should be: >From 712883d0151222a276f777f473d96aa23ad5d9d6 Mon Sep 17 00:00:00 2001 From: Hu Tao <hutao(a)cn.fujitsu.com&gt; Date: Tue, 12 Apr 2011 18:29:27 +0800 Subject: [PATCH] qemu: fix a dead-lock problem In qemuDomainObjBeginJobWithDriver, when virCondWaitUntil timeouts, the function tries to call qemuDriverLock with virDomainObj locked, this causes the dead-lock problem. This patch fixes this. --- src/qemu/qemu_domain.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c index c2a1f9a..a947b4e 100644 --- a/src/qemu/qemu_domain.c +++ b/src/qemu/qemu_domain.c @@ -506,15 +506,17 @@ int qemuDomainObjBeginJobWithDriver(struct qemud_driver *driver, while (priv->jobActive) { if (virCondWaitUntil(&priv->jobCond, &obj->lock, then) < 0) { - /* Safe to ignore value since ref count was incremented above */ - ignore_value(virDomainObjUnref(obj)); if (errno == ETIMEDOUT) qemuReportError(VIR_ERR_OPERATION_TIMEOUT, "%s", _("cannot acquire state change lock")); else virReportSystemError(errno, "%s", _("cannot acquire job mutex")); + virDomainObjUnlock(obj); qemuDriverLock(driver); + virDomainObjLock(obj); + /* Safe to ignore value since ref count was incremented above */ + ignore_value(virDomainObjUnref(obj)); return -1; } } --