Re: [PATCH v3] KVM: Move VM's worker kthreads back to the original cgroup before exiting.

kernel test robot
2022-02-17T12:34:56Z

Hi Vipin,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on db6e7adf8de9b3b99a9856acb73870cc3a70e3ca]

url: https://github.com/0day-ci/linux/commits/Vipin-Sharma/KVM-Move-VM-s-worker-kthreads-back-to-the-original-cgroup-before-exiting/20220217-141723
base: db6e7adf8de9b3b99a9856acb73870cc3a70e3ca
config: s390-randconfig-s032-20220217 (https://download.01.org/0day-ci/archive/20220217/202202172046.GuW8pHQc-lkp@intel.com/config)
compiler: s390-linux-gcc (GCC) 11.2.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# apt-get install sparse
# sparse version: v0.6.4-dirty
# https://github.com/0day-ci/linux/commit/1abffef71ef85b6fb8f1296e6ef38febc4f2b007
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Vipin-Sharma/KVM-Move-VM-s-worker-kthreads-back-to-the-original-cgroup-before-exiting/20220217-141723
git checkout 1abffef71ef85b6fb8f1296e6ef38febc4f2b007
# save the config file to linux build tree
mkdir build_dir
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=s390 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

sparse warnings: (new ones prefixed by >>)
arch/s390/kvm/../../../virt/kvm/kvm_main.c: note: in included file:
include/linux/kvm_host.h:1877:54: sparse: sparse: array of flexible structures
include/linux/kvm_host.h:1879:56: sparse: sparse: array of flexible structures
>> arch/s390/kvm/../../../virt/kvm/kvm_main.c:5859:54: sparse: sparse: incorrect type in argument 1 (different address spaces) @@ expected struct task_struct *from @@ got struct task_struct [noderef] __rcu *real_parent @@
arch/s390/kvm/../../../virt/kvm/kvm_main.c:5859:54: sparse: expected struct task_struct *from
arch/s390/kvm/../../../virt/kvm/kvm_main.c:5859:54: sparse: got struct task_struct [noderef] __rcu *real_parent
arch/s390/kvm/../../../virt/kvm/kvm_main.c:2522:9: sparse: sparse: context imbalance in 'hva_to_pfn_remapped' - unexpected unlock

vim +5859 arch/s390/kvm/../../../virt/kvm/kvm_main.c

5805
5806 static int kvm_vm_worker_thread(void *context)
5807 {
5808 /*
5809 * The init_context is allocated on the stack of the parent thread, so
5810 * we have to locally copy anything that is needed beyond initialization
5811 */
5812 struct kvm_vm_worker_thread_context *init_context = context;
5813 struct kvm *kvm = init_context->kvm;
5814 kvm_vm_thread_fn_t thread_fn = init_context->thread_fn;
5815 uintptr_t data = init_context->data;
5816 int err, reattach_err;
5817
5818 err = kthread_park(current);
5819 /* kthread_park(current) is never supposed to return an error */
5820 WARN_ON(err != 0);
5821 if (err)
5822 goto init_complete;
5823
5824 err = cgroup_attach_task_all(init_context->parent, current);
5825 if (err) {
5826 kvm_err("%s: cgroup_attach_task_all failed with err %d\n",
5827 __func__, err);
5828 goto init_complete;
5829 }
5830
5831 set_user_nice(current, task_nice(init_context->parent));
5832
5833 init_complete:
5834 init_context->err = err;
5835 complete(&init_context->init_done);
5836 init_context = NULL;
5837
5838 if (err)
5839 goto out;
5840
5841 /* Wait to be woken up by the spawner before proceeding. */
5842 kthread_parkme();
5843
5844 if (!kthread_should_stop())
5845 err = thread_fn(kvm, data);
5846
5847 out:
5848 /*
5849 * Move kthread back to its original cgroup to prevent it lingering in
5850 * the cgroup of the VM process, after the latter finishes its
5851 * execution.
5852 *
5853 * kthread_stop() waits on the 'exited' completion condition which is
5854 * set in exit_mm(), via mm_release(), in do_exit(). However, the
5855 * kthread is removed from the cgroup in the cgroup_exit() which is
5856 * called after the exit_mm(). This causes the kthread_stop() to return
5857 * before the kthread actually quits the cgroup.
5858 */
> 5859 reattach_err = cgroup_attach_task_all(current->real_parent, current);
5860 if (reattach_err) {
5861 kvm_err("%s: cgroup_attach_task_all failed on reattach with err %d\n",
5862 __func__, reattach_err);
5863 }
5864 return err;
5865 }
5866

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0-DAY CI Kernel Test Service, Intel Corporation