Re: [linux-pm] 2.6.21-rc4-mm1: freezing of processes broken

[Oleg Nesterov]

On 03/21, Nigel Cunningham wrote:
> 
> On Tue, 2007-03-20 at 19:23 -0600, Eric W. Biederman wrote:
> > >> > Rafael J. Wysocki napsal(a):
> > >
> > > Bisection shows that the freezing of processes has been broken by one of the
> > > patches:
> > >
> > > remove-the-likelypid-check-in-copy_process.patch
> > 
> > Grr.  Oleg's review of remove-the-likelypid-check-in-copy-process
> > showed it to be questionable (and it was just an optimization)
> > so we can get rid of that one easily. 
> > 
> > Although all it did that was really questionable was add
> > the idle process to the global process list and bump a process
> > count when we forked the idle process.  Not dramatically dangerous
> > things.
> 
> Could the freezer code be trying to freeze the idle thread as a result?

Yes. remove-the-likelypid-check-in-copy_process.patch make idle threads
visible to for_each_process/do_each_thread. Note also that idle threads
have ->mm != NULL. freezer, oom_kill, move_task_off_dead_cpu, etc, should
not see idle threads, but they do now.

Oleg.

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