Re: [libvirt] [PATCH 1/5] qemu: Do not access stale data in virDomainBlockStats

https://bugzilla.redhat.com/show_bug.cgi?id=1043069 When virDomainDetachDeviceFlags is called concurrently to virDomainBlockStats: libvirtd may crash because qemuDomainBlockStats finds a disk in vm->def before getting a job on a domain and uses the disk pointer after getting the job. However, the domain in unlocked while waiting on a job condition and thus data behind the disk pointer may disappear. This happens when thread 1 runs virDomainDetachDeviceFlags and enters monitor to actually remove the disk. Then another thread starts running virDomainBlockStats, finds the disk in vm->def, and while it's waiting on the job condition (owned by the first thread), the first thread finishes the disk removal. When the second thread gets the job, the memory pointed to be the disk pointer is already gone. That said, every API that is going to begin a job should do that before fetching data from vm->def.