Messages in this thread | | | Date | Fri, 25 Feb 2022 18:37:35 +0100 | From | Michal Koutný <> | Subject | Re: [PATCH v2] KVM: Move VM's worker kthreads back to the original cgroups before exiting. |
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Hi Vipin.
On Wed, Feb 16, 2022 at 09:37:45AM -0800, Vipin Sharma <vipinsh@google.com> wrote: > On Thu, Jan 20, 2022 at 7:05 AM Michal Koutný <mkoutny@suse.com> wrote: > > Have I missed an obstacle?
Aha...
[ > I used few other combination where I put kernel_wait() call after > put_task_struct(k) call. > > Every time during the module exit, kernel was crashing like:
Thanks for trying this out. ]
> Do you have any suggestions what might be the right way to use this API?
...it has occured to me now -- the KVM kthread is not a child of the wanna-wait user task. So the kernel_wait() silently errs with -ECHILD and task_struct is released too early and that (probably) brings about the crash.
I'm sorry for not realizing that initially.
(Generally, any kthread_create'd task would be affected by this. I guess the KVM worker threads can't be forked from the kvm_create_vm() callers? (It could prevent the double migration to and from caller's cgroup though.))
Michal
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