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SubjectRe: [PATCH V2 1/4] kthread: add a mechanism to store cgroup info
Hello,

On Wed, Sep 13, 2017 at 02:01:26PM -0700, Shaohua Li wrote:
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 26db528..3107eee 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -20,7 +20,6 @@
> #include <linux/freezer.h>
> #include <linux/ptrace.h>
> #include <linux/uaccess.h>
> -#include <linux/cgroup.h>
> #include <trace/events/sched.h>
>
> static DEFINE_SPINLOCK(kthread_create_lock);
> @@ -47,6 +46,7 @@ struct kthread {
> void *data;
> struct completion parked;
> struct completion exited;

maybe #ifdef CONFIG_CGROUPS?

> + struct cgroup_subsys_state *blkcg_css;
> };
...
> +void kthread_associate_blkcg(struct cgroup_subsys_state *css)
> +{
> + struct kthread *kthread;
> +
> + if (!(current->flags & PF_KTHREAD) || !current->set_child_tid)
> + return;
> + kthread = to_kthread(current);
> + if (css) {
> + css_get(css);
> + kthread->blkcg_css = css;
> + } else if (kthread->blkcg_css) {
> + css_put(kthread->blkcg_css);
> + kthread->blkcg_css = NULL;
> + }
> +}
> +EXPORT_SYMBOL(kthread_associate_blkcg);

Maybe doing sth like the following is less error-prone?

kthread_associate_blkcg(@css)
{
if (current's kthread->blkcg_css)
put kthread->blkcg_css and set it to NULL;
if (@css)
get @css and set kthread->blkcg;
}

Thanks.

--
tejun

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