From: Sean Christopherson <seanjc@google.com>
To: Vipin Sharma <vipinsh@google.com>
Cc: pbonzini@redhat.com, dmatlack@google.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: Move VM's worker kthreads back to the original cgroups before exiting.
Date: Tue, 14 Dec 2021 17:16:31 +0000 [thread overview]
Message-ID: <YbjRb0XR7neyX/Gy@google.com> (raw)
In-Reply-To: <20211214050708.4040200-1-vipinsh@google.com>
On Tue, Dec 14, 2021, Vipin Sharma wrote:
> VM worker kthreads can linger in the VM process's cgroup for sometime
> after KVM temrinates the VM process.
>
> KVM terminates the worker kthreads by calling kthread_stop() which waits
> on the signal generated by exit_mm() in do_exit() during kthread's exit.
> However, these kthreads are removed from the cgroup using cgroup_exit()
> call which happens after exit_mm() in do_exit(). A VM process can
> terminate between the time window of exit_mm() to cgroup_exit(), leaving
> only worker kthreads in the cgroup.
>
> Moving worker kthreads back to the original cgroup (kthreadd_task's
> cgroup) makes sure that cgroup is empty as soon as the main VM process
> is terminated.
>
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> ---
> virt/kvm/kvm_main.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index b0f7e6eb00ff..edd304a18f16 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -5785,7 +5785,7 @@ static int kvm_vm_worker_thread(void *context)
> init_context = NULL;
>
> if (err)
> - return err;
> + goto out;
>
> /* Wait to be woken up by the spawner before proceeding. */
> kthread_parkme();
> @@ -5793,6 +5793,15 @@ static int kvm_vm_worker_thread(void *context)
> if (!kthread_should_stop())
> err = thread_fn(kvm, data);
>
> +out:
> + /*
> + * We need to move the kthread back to its original cgroups, so that it
> + * doesn't linger in the cgroups of the user process after that has
> + * already terminated. exit_mm() in do_exit() signals kthread_stop() to
> + * return, whereas, removal of the task from the cgroups happens in
> + * cgroup_exit() which happens after exit_mm().
> + */
> + WARN_ON(cgroup_attach_task_all(kthreadd_task, current));
As the build bot noted, kthreadd_task isn't exported, and I doubt you'll convince
folks to let you export it.
Why is it problematic for the kthread to linger in the cgroup? Conceptually, it's
not really wrong.
> return err;
> }
>
>
> base-commit: d8f6ef45a623d650f9b97e11553adb4978f6aa70
> --
> 2.34.1.173.g76aa8bc2d0-goog
>
next prev parent reply other threads:[~2021-12-14 17:16 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-14 5:07 [PATCH] KVM: Move VM's worker kthreads back to the original cgroups before exiting Vipin Sharma
2021-12-14 15:46 ` kernel test robot
2021-12-14 16:14 ` Lai Jiangshan
2021-12-22 20:14 ` Vipin Sharma
2021-12-14 17:16 ` Sean Christopherson [this message]
2021-12-15 3:58 ` Vipin Sharma
2021-12-14 17:44 ` kernel test robot
2021-12-15 18:27 ` Paolo Bonzini
2021-12-22 20:12 ` Vipin Sharma
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YbjRb0XR7neyX/Gy@google.com \
--to=seanjc@google.com \
--cc=dmatlack@google.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=vipinsh@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).