The following patches were made over linus's tree and also apply over Jens's 5.15 io_ring branch and Michael's vhost branch.
The patchset allows the vhost layer to do a copy_process on the thread that does the VHOST_SET_OWNER ioctl like how io_uring does a copy_process against its userspace app (Jens, the patches make create_io_thread more generic so that's why you are cc'd). This allows the vhost layer's worker threads to inherit cgroups, namespaces, address space, etc and this worker thread will also be accounted for against that owner/parent process's RLIMIT_NPROC limit. Here is a more detailed problem description: Qemu will create vhost devices in the kernel which perform network, SCSI, etc IO and management operations from worker threads created by the kthread API. Because the kthread API does a copy_process on the kthreadd thread, the vhost layer has to use kthread_use_mm to access the Qemu thread's memory and cgroup_attach_task_all to add itself to the Qemu thread's cgroups. The problem with this approach is that we then have to add new functions/ args/functionality for every thing we want to inherit. I started doing that here: https://lkml.org/lkml/2021/6/23/1233 for the RLIMIT_NPROC check, but it seems it might be easier to just inherit everything from the beginning, becuase I'd need to do something like that patch several times. For example, the current approach does not support cgroups v2 so commands like virsh emulatorpin do not work. The qemu process can go over its RLIMIT_NPROC. And for future vhost interfaces where we export the vhost thread pid we will want the namespace info. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
