On 05/12, Rafael J. Wysocki wrote:
>
> Ah, I see. We spawn a kernel thread from a code path that belongs to a
> user space task and we need to call deamonize() to make it become a
> 'real' kernel thread.
>
> Still, this means that is_user_space() may return 'true' for this thread
> before it calls daemonize() and then the scenario described by me in the
> previous message may occur. It seems.
Yes sure. Probably not so bad in practice. Most likely this fresh thread
is not "important" and could be freezed, I dunno.
> It's in freezer-fix-pf_nofreeze-vs-freezeable-race.patch (appended for
> convenience, white space may be broken).
>
> ---
> --- a/include/linux/freezer.h~freezer-fix-pf_nofreeze-vs-freezeable-race
> +++ a/include/linux/freezer.h
> @@ -63,8 +63,10 @@ static inline int thaw_process(struct ta
> */
> static inline void frozen_process(struct task_struct *p)
> {
> - p->flags |= PF_FROZEN;
> - wmb();
> + if (!unlikely(p->flags & PF_NOFREEZE)) {
> + p->flags |= PF_FROZEN;
> + wmb();
> + }
> clear_tsk_thread_flag(p, TIF_FREEZE);
> }
This is OK if a kernel thread does try_to_freeze() eventually.
But what if it does not, because it marks itself as PF_NOFREEZE?
This means it may run with signal_pending() forever. That is why
I think we should clear TIF_FREEZE when we set PF_NOFREEZE.
Oleg.
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