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Date: Mon, 4 Oct 2021 09:12:49 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Mike Christie <michael.christie@...cle.com>
Cc: hdanton@...a.com, hch@...radead.org, stefanha@...hat.com,
jasowang@...hat.com, sgarzare@...hat.com,
virtualization@...ts.linux-foundation.org,
christian.brauner@...ntu.com, axboe@...nel.dk,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 9/9] vhost: use kernel_worker to check RLIMITs and
inherit v2 cgroups
On Tue, Sep 21, 2021 at 04:52:18PM -0500, Mike Christie wrote:
> For vhost workers we use the kthread API which inherit's its values from
> and checks against the kthreadd thread. This results in cgroups v2 not
> working and the wrong RLIMITs being checked. This patch has us use the
> kernel_copy_process function which will inherit its values/checks from the
> thread that owns the device.
>
> Signed-off-by: Mike Christie <michael.christie@...cle.com>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
Feel free to merge with other bits.
> ---
> drivers/vhost/vhost.c | 68 ++++++++++++++++---------------------------
> drivers/vhost/vhost.h | 7 ++++-
> 2 files changed, 31 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index c9a1f706989c..7a5142dcde1b 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -22,7 +22,6 @@
> #include <linux/slab.h>
> #include <linux/vmalloc.h>
> #include <linux/kthread.h>
> -#include <linux/cgroup.h>
> #include <linux/module.h>
> #include <linux/sort.h>
> #include <linux/sched/mm.h>
> @@ -344,17 +343,14 @@ static void vhost_vq_reset(struct vhost_dev *dev,
> static int vhost_worker(void *data)
> {
> struct vhost_worker *worker = data;
> - struct vhost_dev *dev = worker->dev;
> struct vhost_work *work, *work_next;
> struct llist_node *node;
>
> - kthread_use_mm(dev->mm);
> -
> for (;;) {
> /* mb paired w/ kthread_stop */
> set_current_state(TASK_INTERRUPTIBLE);
>
> - if (kthread_should_stop()) {
> + if (test_bit(VHOST_WORKER_FLAG_STOP, &worker->flags)) {
> __set_current_state(TASK_RUNNING);
> break;
> }
> @@ -376,8 +372,9 @@ static int vhost_worker(void *data)
> schedule();
> }
> }
> - kthread_unuse_mm(dev->mm);
> - return 0;
> +
> + complete(worker->exit_done);
> + do_exit(0);
> }
>
> static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
> @@ -517,31 +514,6 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
> }
> EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
>
> -struct vhost_attach_cgroups_struct {
> - struct vhost_work work;
> - struct task_struct *owner;
> - int ret;
> -};
> -
> -static void vhost_attach_cgroups_work(struct vhost_work *work)
> -{
> - struct vhost_attach_cgroups_struct *s;
> -
> - s = container_of(work, struct vhost_attach_cgroups_struct, work);
> - s->ret = cgroup_attach_task_all(s->owner, current);
> -}
> -
> -static int vhost_attach_cgroups(struct vhost_dev *dev)
> -{
> - struct vhost_attach_cgroups_struct attach;
> -
> - attach.owner = current;
> - vhost_work_init(&attach.work, vhost_attach_cgroups_work);
> - vhost_work_queue(dev, &attach.work);
> - vhost_work_dev_flush(dev);
> - return attach.ret;
> -}
> -
> /* Caller should have device mutex */
> bool vhost_dev_has_owner(struct vhost_dev *dev)
> {
> @@ -579,6 +551,16 @@ static void vhost_detach_mm(struct vhost_dev *dev)
> dev->mm = NULL;
> }
>
> +static void vhost_worker_stop(struct vhost_worker *worker)
> +{
> + DECLARE_COMPLETION_ONSTACK(exit_done);
> +
> + worker->exit_done = &exit_done;
> + set_bit(VHOST_WORKER_FLAG_STOP, &worker->flags);
> + wake_up_process(worker->task);
> + wait_for_completion(worker->exit_done);
> +}
> +
> static void vhost_worker_free(struct vhost_dev *dev)
> {
> struct vhost_worker *worker = dev->worker;
> @@ -588,7 +570,7 @@ static void vhost_worker_free(struct vhost_dev *dev)
>
> dev->worker = NULL;
> WARN_ON(!llist_empty(&worker->work_list));
> - kthread_stop(worker->task);
> + vhost_worker_stop(worker);
> kfree(worker);
> }
>
> @@ -603,27 +585,27 @@ static int vhost_worker_create(struct vhost_dev *dev)
> return -ENOMEM;
>
> dev->worker = worker;
> - worker->dev = dev;
> worker->kcov_handle = kcov_common_handle();
> init_llist_head(&worker->work_list);
>
> - task = kthread_create(vhost_worker, worker, "vhost-%d", current->pid);
> + /*
> + * vhost used to use the kthread API which ignores all signals by
> + * default and the drivers expect this behavior. So we do not want to
> + * ineherit the parent's signal handlers and set our worker to ignore
> + * everything below.
> + */
> + task = kernel_worker(vhost_worker, worker, NUMA_NO_NODE,
> + CLONE_FS | CLONE_CLEAR_SIGHAND,
> + KERN_WORKER_NO_FILES | KERN_WORKER_NO_SIGS);
> if (IS_ERR(task)) {
> ret = PTR_ERR(task);
> goto free_worker;
> }
>
> worker->task = task;
> - wake_up_process(task); /* avoid contributing to loadavg */
> -
> - ret = vhost_attach_cgroups(dev);
> - if (ret)
> - goto stop_worker;
> -
> + kernel_worker_start(task, "vhost-%d", current->pid);
> return 0;
>
> -stop_worker:
> - kthread_stop(worker->task);
> free_worker:
> kfree(worker);
> dev->worker = NULL;
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 102ce25e4e13..09748694cb66 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -25,11 +25,16 @@ struct vhost_work {
> unsigned long flags;
> };
>
> +enum {
> + VHOST_WORKER_FLAG_STOP,
> +};
> +
> struct vhost_worker {
> struct task_struct *task;
> + struct completion *exit_done;
> struct llist_head work_list;
> - struct vhost_dev *dev;
> u64 kcov_handle;
> + unsigned long flags;
> };
>
> /* Poll a file (eventfd or socket) */
> --
> 2.25.1
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