Messages in this thread |  | | From | "Rafael J. Wysocki" <> | Subject | Re: [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug | Date | Sun, 18 Feb 2007 11:32:39 +0100 |
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On Sunday, 18 February 2007 00:42, Oleg Nesterov wrote: > On 02/17, Rafael J. Wysocki wrote: > > > > On Saturday, 17 February 2007 22:34, Oleg Nesterov wrote: > > > > > > static inline int is_user_space(struct task_struct *p) > > > { > > > return p->mm && !(p->flags & PF_BORROWED_MM); > > > } > > > > > > This doesn't look right. First, an exiting task has ->mm == NULL after > > > do_exit()->exit_mm(). Probably not a problem. However, PF_BORROWED_MM > > > check is racy without task_lock(), so we can have a false positive as > > > well. Is it ok? We can freeze aio_wq prematurely. > > > > Right now aio_wq is not freezeable (PF_NOFREEZE). > > Right now yes, but we are going to change this?
Well, is there any more reliable (and not racy) method of differentiating between kernel threads and user space processes?
> > > cancel_freezing(p); > > > continue; > > > > > > Is it right? Shouldn't we increment "todo" counter? > > > > No. It would be wrong to do that, because TASK_TRACED tasks with frozen > > parents cannot be frozen any further. > > TASK_TRACED task could be woken by SIGKILL. cancel_freezing() clears TIF_FREEZE. > The task may start do_exit() when try_to_freeze_tasks() returns "success". > Probably not a problem.
Yup.
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