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sched: Make the idle task quack like a per-CPU kthread

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For all intents and purposes, the idle task is a per-CPU kthread. It isn't
created via the same route as other pcpu kthreads however, and as a result
it is missing a few bells and whistles: it fails kthread_is_per_cpu() and
it doesn't have PF_NO_SETAFFINITY set.

Fix the former by giving the idle task a kthread struct along with the
KTHREAD_IS_PER_CPU flag. This requires some extra iffery as init_idle()
call be called more than once on the same idle task.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210510151024.2448573-2-valentin.schneider@arm.com
This commit is contained in:
Valentin Schneider
2021-05-10 16:10:23 +01:00
committed by Peter Zijlstra
parent fcb5017045
commit 00b89fe019
3 changed files with 35 additions and 18 deletions
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kernel/kthread.c
+18 -12
View File
@@ -68,16 +68,6 @@ enum KTHREAD_BITS {
KTHREAD_SHOULD_PARK,
};
static inline void set_kthread_struct(void *kthread)
{
/*
* We abuse ->set_child_tid to avoid the new member and because it
* can't be wrongly copied by copy_process(). We also rely on fact
* that the caller can't exec, so PF_KTHREAD can't be cleared.
*/
current->set_child_tid = (__force void __user *)kthread;
}
static inline struct kthread *to_kthread(struct task_struct *k)
{
WARN_ON(!(k->flags & PF_KTHREAD));
@@ -103,6 +93,22 @@ static inline struct kthread *__to_kthread(struct task_struct *p)
return kthread;
}
void set_kthread_struct(struct task_struct *p)
{
struct kthread *kthread;
if (__to_kthread(p))
return;
kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
/*
* We abuse ->set_child_tid to avoid the new member and because it
* can't be wrongly copied by copy_process(). We also rely on fact
* that the caller can't exec, so PF_KTHREAD can't be cleared.
*/
p->set_child_tid = (__force void __user *)kthread;
}
void free_kthread_struct(struct task_struct *k)
{
struct kthread *kthread;
@@ -272,8 +278,8 @@ static int kthread(void *_create)
struct kthread *self;
int ret;
self = kzalloc(sizeof(*self), GFP_KERNEL);
set_kthread_struct(self);
set_kthread_struct(current);
self = to_kthread(current);
/* If user was SIGKILLed, I release the structure. */
done = xchg(&create->done, NULL);