Re: [libvirt] [PATCHv3] qemu: fix crash when mixing sync and async monitor jobs

Currently, we attempt to run sync job and async job at the same time. It means that the monitor commands for two jobs can be run in any order. In the function qemuDomainObjEnterMonitorInternal(): if (priv->job.active == QEMU_JOB_NONE && priv->job.asyncJob) { if (qemuDomainObjBeginNestedJob(driver, obj) < 0) We check whether the caller is an async job by priv->job.active and priv->job.asynJob. But when an async job is running, and a sync job is also running at the time of the check, then priv->job.active is not QEMU_JOB_NONE. So we cannot check whether the caller is an async job in the function qemuDomainObjEnterMonitorInternal(), and must instead put the burden on the caller to tell us when an async command wants to do a nested job. Once the burden is on the caller, then only async monitor enters need to worry about whether the VM is still running; for sync monitor enter, the internal return is always 0, so lots of ignore_value can be dropped. * src/qemu/THREADS.txt: Reflect new rules. * src/qemu/qemu_domain.h (qemuDomainObjEnterMonitorAsync): New prototype. * src/qemu/qemu_process.h (qemuProcessStartCPUs) (qemuProcessStopCPUs): Add parameter. * src/qemu/qemu_migration.h (qemuMigrationToFile): Likewise. (qemuMigrationWaitForCompletion): Make static. * src/qemu/qemu_domain.c (qemuDomainObjEnterMonitorInternal): Add parameter. (qemuDomainObjEnterMonitorAsync): New function. (qemuDomainObjEnterMonitor, qemuDomainObjEnterMonitorWithDriver): Update callers. * src/qemu/qemu_driver.c (qemuDomainSaveInternal) (qemudDomainCoreDump, doCoreDump, processWatchdogEvent) (qemudDomainSuspend, qemudDomainResume, qemuDomainSaveImageStartVM) (qemuDomainSnapshotCreateActive, qemuDomainRevertToSnapshot): Likewise. * src/qemu/qemu_process.c (qemuProcessStopCPUs) (qemuProcessFakeReboot, qemuProcessRecoverMigration) (qemuProcessRecoverJob, qemuProcessStart): Likewise. * src/qemu/qemu_migration.c (qemuMigrationToFile) (qemuMigrationWaitForCompletion, qemuMigrationUpdateJobStatus) (qemuMigrationJobStart, qemuDomainMigrateGraphicsRelocate) (doNativeMigrate, doTunnelMigrate, qemuMigrationPerformJob) (qemuMigrationPerformPhase, qemuMigrationFinish) (qemuMigrationConfirm): Likewise. * src/qemu/qemu_hotplug.c: Drop unneeded ignore_value. --- v3: incorporate Wen's feedback - in particular, virProcessStartCPUs now checks for return type, restarting libvirt does not use an async job, and I didn't hit the deadlock in the same scenarios as I tested under v2.

I still need to do migration testing before I'm convinced that this is right, but it's doing a lot better.