On Mon, Dec 16, 2024, Juri Lelli wrote: > On 14/12/24 19:52, Peter Zijlstra wrote: > > On Sat, Dec 14, 2024 at 06:32:57AM +0000, Ranguvar wrote: > > > Hello, all, > > > > > > Any assistance with proper format and process is appreciated as I am new > > > to these lists. After the commit bd9bbc96e835 "sched: Rework dl_server" > > > I am no longer able to boot my Windows 11 23H2 guest using > > > pinned/exclusive CPU cores and passing a PCIe graphics card. This setup > > > worked for me since at least 5.10, likely earlier, with minimal changes. > > > > > > Most or all cores assigned to guest VM report 100% usage, and many tasks > > > on the host hang indefinitely (10min+) until the guest is forcibly > > > stopped. This happens only once the Windows kernel begins loading - its > > > spinner appears and freezes. > > > > > > Still broken on 6.13-rc2, as well as 6.12.4 from Arch's repository. When > > > testing these, the failure is similar, but tasks on the host are slow to > > > execute instead of stalling indefinitely, and hung tasks are not reported > > > in dmesg. Only one guest core may show 100% utilization instead of many > > > or all of them. This seems to be due to a separate regression which also > > > impacts my usecase [0]. After patching it [1], I then find the same > > > behavior as bd9bbc96e835, with hung tasks on host. > > > > > > git bisect log: [2] > > > dmesg from 6.11.0-rc1-1-git-00057-gbd9bbc96e835, with decoded hung task backtraces: [3] > > > dmesg from arch 6.12.4: [4] > > > dmesg from arch 6.12.4 patched for svm.c regression, has hung tasks, backtraces could not be decoded: [5] > > > config for 6.11.0-rc1-1-git-00057-gbd9bbc96e835: [6] > > > config for arch 6.12.4: [7] > > > > > > If it helps, my host uses an AMD Ryzen 5950X CPU with latest UEFI and AMD > > > WX 5100 (Polaris, GCN 4.0) PCIe graphics. I use libvirt 10.10 and qemu > > > 9.1.2, and I am passing three PCIe devices each from dedicated IOMMU > > > groups: NVIDIA RTX 3090 graphics, a Renesas uPD720201 USB controller, and > > > a Samsung 970 EVO NVMe disk. > > > > > > I have in kernel cmdline `iommu=pt isolcpus=1-7,17-23 rcu_nocbs=1-7,17-23 > > > nohz_full=1-7,17-23`. Removing iommu=pt does not produce a change, and > > > dropping the core isolation freezes the host on VM startup. As in, dropping all of isolcpus, rcu_nocbs, and nohz_full? Or just dropping isolcpus? > > > Enabling/disabling kvm_amd.nested or kvm.enable_virt_at_load did not > > > produce a change. > > > > > > Thank you for your attention. > > > - Devin > > > > > > #regzbot introduced: bd9bbc96e8356886971317f57994247ca491dbf1 > > > > > > [0]: https://lore.kernel.org/regressions/52914da7-a97b-45ad-86a0-affdf8266c61@xxxxxxxxxxx/ > > > [1]: https://lore.kernel.org/regressions/376c445a-9437-4bdd-9b67-e7ce786ae2c4@xxxxxxxxxxx/ > > > [2]: https://ranguvar.io/pub/paste/linux-6.12-vm-regression/bisect.log > > > [3]: https://ranguvar.io/pub/paste/linux-6.12-vm-regression/dmesg-6.11.0-rc1-1-git-00057-gbd9bbc96e835-decoded.log > > > > Hmm, this has: > > > > [ 978.035637] sched: DL replenish lagged too much > > > > Juri, have we seen that before? > > Not in the context of dl_server. Hummm, looks like replenishment wasn't > able to catch up with the clock or something like that (e.g. > replenishment didn't happen for a long time). I don't see anything in the logs that suggests KVM is doing something funky. My guess is that the issue is related to isolcpus+rcu_nocbs+nohz_full, and that KVM setups are one of the more common use cases for such configurations. But that's just a wild guess on my part. The hang from [4] occurs because KVM can't complete a memslot update. Given that this shows up with GPU passthrough, odds are good the guest is trying to relocate a GPU bar and the relocation hangs because the KVM-side update hangs. There are some interesting/unique paths in KVM's memslot code, but this is a simple hang on SRCU synchronization. INFO: task CPU 0/KVM:2134 blocked for more than 122 seconds. Not tainted 6.11.0-rc1-1-git-00057-gbd9bbc96e835 #12 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:CPU 0/KVM state:D stack:0 pid:2134 tgid:2114 ppid:1 flags:0x00004002 Call Trace: <TASK> __schedule (kernel/sched/core.c:5258 kernel/sched/core.c:6594) schedule (./arch/x86/include/asm/preempt.h:84 (discriminator 13) kernel/sched/core.c:6672 (discriminator 13) kernel/sched/core.c:6686 (discriminator 13)) schedule_timeout (kernel/time/timer.c:2558) wait_for_completion (kernel/sched/completion.c:96 kernel/sched/completion.c:116 kernel/sched/completion.c:127 kernel/sched/completion.c:148) __synchronize_srcu (kernel/rcu/srcutree.c:1408) kvm_swap_active_memslots+0x133/0x180 kvm kvm_set_memslot+0x3de/0x680 kvm kvm_vm_ioctl+0x11da/0x18d0 kvm __x64_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:907 fs/ioctl.c:893 fs/ioctl.c:893) do_syscall_64 (arch/x86/entry/common.c:52 (discriminator 1) arch/x86/entry/common.c:83 (discriminator 1)) And in [5], the host hang that first pops is also on wait_for_completion(), in code that is potentially trying to queue work on all CPUs (I've no idea if cpu_needs_drain() can be true on the isolated CPUs). cpumask_clear(&has_work); for_each_online_cpu(cpu) { struct work_struct *work = &per_cpu(lru_add_drain_work, cpu); if (cpu_needs_drain(cpu)) { INIT_WORK(work, lru_add_drain_per_cpu); queue_work_on(cpu, mm_percpu_wq, work); __cpumask_set_cpu(cpu, &has_work); } } for_each_cpu(cpu, &has_work) flush_work(&per_cpu(lru_add_drain_work, cpu)); sched: DL replenish lagged too much systemd[1]: Starting Cleanup of Temporary Directories... systemd[1]: systemd-tmpfiles-clean.service: Deactivated successfully. systemd[1]: Finished Cleanup of Temporary Directories. systemd[1]: systemd-journald.service: State 'stop-watchdog' timed out. Killing. systemd[1]: systemd-journald.service: Killing process 647 (systemd-journal) with signal SIGKILL. systemd[1]: Starting system activity accounting tool... systemd[1]: sysstat-collect.service: Deactivated successfully. systemd[1]: Finished system activity accounting tool. INFO: task khugepaged:263 blocked for more than 122 seconds. Not tainted 6.12.4-arch1-1 #1 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:khugepaged state:D stack:0 pid:263 tgid:263 ppid:2 flags:0x00004000 Call Trace: <TASK> __schedule+0x3b0/0x12b0 schedule+0x27/0xf0 schedule_timeout+0x12f/0x160 wait_for_completion+0x86/0x170 __flush_work+0x1bf/0x2c0 __lru_add_drain_all+0x13e/0x1e0 khugepaged+0x66/0x930 kthread+0xd2/0x100 ret_from_fork+0x34/0x50 ret_from_fork_asm+0x1a/0x30 </TASK>
