Re: [libvirt] [BUG] qemu quited unexpectedly will cause libvirtd crashed

>> So I try to use gdb and add sleep() to trigger this bug. I have posted two patches >> to fix 2 bugs. But there is still another bug, and I have no good way to fix it. > >> Steps to reproduce this bug: >> 1. use gdb to attach libvirtd, and set a breakpoint in the function >> qemuConnectMonitor() >> 2. start a vm >> 3. let the libvirtd to run until qemuMonitorSetCapabilities() returns. >> 4. kill the qemu process >> 5. step into qemuDomainObjExitMonitorWithDriver(), and set debug to 1 >> >> Now, qemuDomainObjExitMonitorWithDriver() will sleep 100s to make sure >> qemuProcessHandleMonitorEOF() is done before qemuProcessHandleMonitorEOF() >> returns. >> >> priv->mon will be null after qemuDomainObjExitMonitorWithDriver() returns. >> So we must not use it. Unfortunately we still use it, and it will cause >> libvirtd crashed. > > Sounds like qemuConnectMonitor needs an extra reference around priv->mon > for the duration of the connect attempt, so that > qemuProcessHandleMonitorEOF will not free the monitor. No, qemuConnectMonitor() calls qemuDomainObjEnterMonitorWithDriver() to hold an extra reference around priv->mon, and release it in qemuDomainObjExitMonitorWithDriver(). But qemuDomainObjExitMonitorWithDriver() does not tell the caller whether priv->mon can be used. If we will call qemuDomainObjEnterMonitorWithDriver()/qemuDomainObjEnterMonitor(), I think we must check whether the domain is active. If we call them more than once, we must check it every time. And we should not do other things between checking whether the domain is active and calling them(If we do as this, the code can be maintained easily)

But some codes does not respect this rule. Here is the list of the functions that may have the similar problem: 1. qemu_migration.c doNativeMigrate() qemuMigrationToFile()