On 2020/7/24 21:11, Daniel Henrique Barboza wrote: > > > On 7/19/20 11:09 PM, Bihong Yu wrote: >> >> >> On 2020/7/18 5:14, Daniel Henrique Barboza wrote: >>> >>> >>> On 7/17/20 8:10 AM, Bihong Yu wrote: >>>>> From c328ff62b11d58553fd2032a85fd3295e009b3d3 Mon Sep 17 00:00:00 2001 >>>> From: Bihong Yu <yubihong@xxxxxxxxxx> >>>> Date: Fri, 17 Jul 2020 16:55:12 +0800 >>>> Subject: [PATCH] qemu: clear residual QMP caps processes during QEMU driver >>>> initialization >>>> >>>> In some cases, the QMP capabilities processes possible residue. So we need to >>>> clear the residual QMP caps processes during starting libvirt. >>> >>> Which cases are you referring to? Do you have a reproducer for this behavior? I >>> tried it up starting and stopping libvirtd, fetching capabilities, starting vms >>> and so on, and wasn't able to see any 'qmp.pid' file hanging around. >> >> Yes, I have a reproducer for this behavior. I refer case is that send kill signal >> to libvirtd when libvirtd is fetching capabilities before libvirtd calling >> qemuProcessQMPFree() and qemuProcessQMPStop(). >> >> When libvirtd restart, it can not find the temporary qmp directory and has no way >> to clear the residual QMP caps processes. > > I see. The reproducer is an abnormal termination of the Libvirt daemon (I'm assuming > SIGKILL - SIGTERM would have been handled). > > The problem is that processes in general can't handle SIGKILL with cleanup functions > (there are gimmicks, but one process can't avoid to not get killed instantly with > a SIGKILL by itself). I don't believe Libvirt can contemplate each cleanup scenario > where a program is terminated with SIGKILL. > > You found one case where a kill -9 left stuff behind, but I guarantee you that there > are many places and situations where this will occur. Basically each temporary file > Libvirt creates are susceptible to this. Yes, I see. But, this abnormal termination will cause the QMP caps processes residue, and could residue many processes if reproduce this abnormal termination. They will waste the system resources. In addition, g_mkdtemp() is used only in one place where the qemuProcessQMPInit() function use to make qmp-XXXXXX temporary directory. If libvirtd exit abnormally, libvirtd will lost control of the temporary directory. In my opition: a. The temporary directory will cause residual processes not only temporary directory itself. b. Libvirtd use g_mkdtemp() only in one place, and will lost control of the temporary directory if libvirtd exit abnormally. So I think it's necessary to clear the residual QMP caps processes and the temporary directory. > > Your proposed fix doesn't help in the case you're trying to cover either. What if > I land a SIGKILL while the code is trying to cleanup the leftovers of the previous > SIGKILL? Now imagine that each place where Libvirt creates a temporary file would > need a cleanup code like this, and every one of them is susceptible to this same > behavior. In my opinion, the other temporary file will be reuse or overwrite if libvirtd restart and it will not cause process residual. Thanks, Bihong Yu > > I am not sure why you needed to kill the process with SIGKILL instead of SIGTERM, > but I'd rather try to understand and fix what lead you to send a -9 to libvirtd > instead. > > > Thanks, > > > DHB
