On Wed, 26 Oct 2016, Oleg Nesterov wrote:
> Some notes right now. Of course, with this patch we are ready to remove
> put_task_stack() from kthread.c right now. The next change should kill
> to_live_kthread() altogether. And stop using ->vfork_done.
>
> And. With this patch we do not need another "workqueue: ignore dead tasks
> in a workqueue sleep hook" fix from Roman.
Nice !
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index be2cc1f..c6adbde 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -53,14 +53,34 @@ enum KTHREAD_BITS {
> KTHREAD_IS_PARKED,
> };
>
> -#define __to_kthread(vfork) \
> - container_of(vfork, struct kthread, exited)
> +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;
Can we pretty please avoid this type casting? We only have 5 places using
set_child_tid. So we can really make it a proper union and fix up the 5
usage sites as a preparatory patch for this.
> +}
>
> static inline struct kthread *to_kthread(struct task_struct *k)
> {
> - return __to_kthread(k->vfork_done);
> + WARN_ON(!(k->flags & PF_KTHREAD));
> + return (__force void *)k->set_child_tid;
> }
>
> +void free_kthread_struct(struct task_struct *k)
> +{
> + kfree(to_kthread(k)); /* can be NULL if kmalloc() failed */
Can you please not use tail comments? They really stop the reading flow.
> +#define __to_kthread(vfork) \
> + container_of(vfork, struct kthread, exited)
> +
> +/*
> + * TODO: kill it and use to_kthread(). But we still need the users
> + * like kthread_stop() which has to sync with the exiting kthread.
> + */
> static struct kthread *to_live_kthread(struct task_struct *k)
> {
> struct completion *vfork = ACCESS_ONCE(k->vfork_done);
> @@ -181,14 +201,11 @@ static int kthread(void *_create)
> int (*threadfn)(void *data) = create->threadfn;
> void *data = create->data;
> struct completion *done;
> - struct kthread self;
> + struct kthread *self;
> int ret;
>
> - self.flags = 0;
> - self.data = data;
> - init_completion(&self.exited);
> - init_completion(&self.parked);
> - current->vfork_done = &self.exited;
> + self = kmalloc(sizeof(*self), GFP_KERNEL);
> + set_kthread_struct(self);
>
> /* If user was SIGKILLed, I release the structure. */
> done = xchg(&create->done, NULL);
> @@ -196,6 +213,19 @@ static int kthread(void *_create)
> kfree(create);
> do_exit(-EINTR);
> }
> +
> + if (!self) {
> + create->result = ERR_PTR(-ENOMEM);
> + complete(done);
> + do_exit(-ENOMEM);
> + }
> +
> + self->flags = 0;
> + self->data = data;
> + init_completion(&self->exited);
> + init_completion(&self->parked);
> + current->vfork_done = &self->exited;
> +
> /* OK, tell user we're spawned, wait for stop or wakeup */
> __set_current_state(TASK_UNINTERRUPTIBLE);
> create->result = current;
> @@ -203,12 +233,10 @@ static int kthread(void *_create)
> schedule();
>
> ret = -EINTR;
> -
> - if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
> - __kthread_parkme(&self);
> + if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
> + __kthread_parkme(self);
> ret = threadfn(data);
> }
> - /* we can't just return, we must preserve "self" on stack */
> do_exit(ret);
> }
Other than the above nits, this is the right direction to go.
Thanks,
tglx
