Messages in this thread | | | Date | Sun, 18 Feb 2007 14:32:59 +0300 | From | Oleg Nesterov <> | Subject | Re: [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug |
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On 02/18, Rafael J. Wysocki wrote: > > 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?
Not that I know of. At least, we can take task_lock() to really rule out kernel threads at FREEZER_USER_SPACE stage.
Oleg.
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