Re: [libvirt] [PATCH] remoteClientCloseFunc: Don't mangle connection object refcount

Well, in 8ad126e6 we tried to fix a memory corruption problem. However, the fix was not as good as it could be. I mean, the commit has one line more than it should. I've noticed this output just recently: # ./run valgrind --leak-check=full --show-reachable=yes ./tools/virsh domblklist gentoo ==17019== Memcheck, a memory error detector ==17019== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. ==17019== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info ==17019== Command: /home/zippy/work/libvirt/libvirt.git/tools/.libs/virsh domblklist gentoo ==17019== Target Source ------------------------------------------------ fda /var/lib/libvirt/images/fd.img vda /var/lib/libvirt/images/gentoo.qcow2 hdc /home/zippy/tmp/install-amd64-minimal-20150402.iso ==17019== Thread 2: ==17019== Invalid read of size 4 ==17019== at 0x4EFF5B4: virObjectUnref (virobject.c:258) ==17019== by 0x5038CFF: remoteClientCloseFunc (remote_driver.c:552) ==17019== by 0x5069D57: virNetClientCloseLocked (virnetclient.c:685) ==17019== by 0x506C848: virNetClientIncomingEvent (virnetclient.c:1852) ==17019== by 0x5082136: virNetSocketEventHandle (virnetsocket.c:1913) ==17019== by 0x4ECD64E: virEventPollDispatchHandles (vireventpoll.c:509) ==17019== by 0x4ECDE02: virEventPollRunOnce (vireventpoll.c:658) ==17019== by 0x4ECBF00: virEventRunDefaultImpl (virevent.c:308) ==17019== by 0x130386: vshEventLoop (vsh.c:1864) ==17019== by 0x4F1EB07: virThreadHelper (virthread.c:206) ==17019== by 0xA8462D3: start_thread (in /lib64/libpthread-2.20.so) ==17019== by 0xAB441FC: clone (in /lib64/libc-2.20.so) ==17019== Address 0x139023f4 is 4 bytes inside a block of size 240 free'd ==17019== at 0x4C2B1F0: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==17019== by 0x4EA8949: virFree (viralloc.c:582) ==17019== by 0x4EFF6D0: virObjectUnref (virobject.c:273) ==17019== by 0x4FE74D6: virConnectClose (libvirt.c:1390) ==17019== by 0x13342A: virshDeinit (virsh.c:406) ==17019== by 0x134A37: main (virsh.c:950) The problem is, when registering remoteClientCloseFunc(), it's conn->closeCallback which is ref'd. But in the function itself it's conn->closeCallback->conn what is unref'd. This is causing imbalance in reference counting. Moreover, there's no need for the remote driver to increase/decrease conn refcount since it's not used anywhere. It's just merely passed to client registered callback. And for that purpose it's correctly ref'd in virConnectRegisterCloseCallback() and then unref'd in virConnectUnregisterCloseCallback(). Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- Not only this is nice because it fixes a bug by removing some lines, it maybe needs to be backported all the way down to v1.0.5 main branches. src/remote/remote_driver.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/src/remote/remote_driver.c b/src/remote/remote_driver.c index ec26ebe..aca00c0 100644 --- a/src/remote/remote_driver.c +++ b/src/remote/remote_driver.c @@ -546,10 +546,6 @@ remoteClientCloseFunc(virNetClientPtr client ATTRIBUTE_UNUSED, cbdata->freeCallback = NULL; } virObjectUnlock(cbdata); - - /* free the connection reference that comes along with the callback - * registration */ - virObjectUnref(cbdata->conn); } /* helper macro to ease extraction of arguments from the URI */ -- 2.4.6