kthread: Generalize pf_io_worker so it can point to struct kthread
The point of using set_child_tid to hold the kthread pointer was that
it already did what is necessary. There are now restrictions on when
set_child_tid can be initialized and when set_child_tid can be used in
schedule_tail. Which indicates that continuing to use set_child_tid
to hold the kthread pointer is a bad idea.
Instead of continuing to use the set_child_tid field of task_struct
generalize the pf_io_worker field of task_struct and use it to hold
the kthread pointer.
Rename pf_io_worker (which is a void * pointer) to worker_private so
it can be used to store kthreads struct kthread pointer. Update the
kthread code to store the kthread pointer in the worker_private field.
Remove the places where set_child_tid had to be dealt with carefully
because kthreads also used it.
Link: https://lkml.kernel.org/r/CAHk-=wgtFAA9SbVYg0gR1tqPMC17-NYcs0GQkaYg1bGhh1uJQQ@mail.gmail.com
Link: https://lkml.kernel.org/r/87a6grvqy8.fsf_-_@email.froward.int.ebiederm.org
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/kernel/kthread.c b/kernel/kthread.c
index c14707d..261a3c3 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -72,7 +72,7 @@ enum KTHREAD_BITS {
static inline struct kthread *to_kthread(struct task_struct *k)
{
WARN_ON(!(k->flags & PF_KTHREAD));
- return (__force void *)k->set_child_tid;
+ return k->worker_private;
}
/*
@@ -80,7 +80,7 @@ static inline struct kthread *to_kthread(struct task_struct *k)
*
* Per construction; when:
*
- * (p->flags & PF_KTHREAD) && p->set_child_tid
+ * (p->flags & PF_KTHREAD) && p->worker_private
*
* the task is both a kthread and struct kthread is persistent. However
* PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
@@ -88,7 +88,7 @@ static inline struct kthread *to_kthread(struct task_struct *k)
*/
static inline struct kthread *__to_kthread(struct task_struct *p)
{
- void *kthread = (__force void *)p->set_child_tid;
+ void *kthread = p->worker_private;
if (kthread && !(p->flags & PF_KTHREAD))
kthread = NULL;
return kthread;
@@ -109,11 +109,7 @@ bool set_kthread_struct(struct task_struct *p)
init_completion(&kthread->parked);
p->vfork_done = &kthread->exited;
- /*
- * We abuse ->set_child_tid to avoid the new member and because it
- * can't be wrongly copied by copy_process().
- */
- p->set_child_tid = (__force void __user *)kthread;
+ p->worker_private = kthread;
return true;
}
@@ -128,7 +124,7 @@ void free_kthread_struct(struct task_struct *k)
#ifdef CONFIG_BLK_CGROUP
WARN_ON_ONCE(kthread && kthread->blkcg_css);
#endif
- k->set_child_tid = (__force void __user *)NULL;
+ k->worker_private = NULL;
kfree(kthread);
}