Re: [patch] oom: thaw threads if oom killed thread is frozen beforedeferring

[Michal Hocko]

On Wed 28-09-11 12:44:45, Michal Hocko wrote:
> On Tue 27-09-11 11:35:04, David Rientjes wrote:
> > On Tue, 27 Sep 2011, Michal Hocko wrote:
> > 
> > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > > index 626303b..c419a7e 100644
> > > --- a/mm/oom_kill.c
> > > +++ b/mm/oom_kill.c
> > > @@ -32,6 +32,7 @@
> > >  #include <linux/mempolicy.h>
> > >  #include <linux/security.h>
> > >  #include <linux/ptrace.h>
> > > +#include <linux/freezer.h>
> > >  
> > >  int sysctl_panic_on_oom;
> > >  int sysctl_oom_kill_allocating_task;
> > > @@ -451,10 +452,15 @@ static int oom_kill_task(struct task_struct *p, struct mem_cgroup *mem)
> > >  				task_pid_nr(q), q->comm);
> > >  			task_unlock(q);
> > >  			force_sig(SIGKILL, q);
> > > +
> > > +			if (frozen(q))
> > > +				thaw_process(q);
> > >  		}
> > >  
> > >  	set_tsk_thread_flag(p, TIF_MEMDIE);
> > >  	force_sig(SIGKILL, p);
> > > +	if (frozen(p))
> > > +		thaw_process(p);
> > >  
> > >  	return 0;
> > >  }
> > 
> > Also needs this...
> > 
> > 
> > oom: thaw threads if oom killed thread is frozen before deferring
> > 
> > If a thread has been oom killed and is frozen, thaw it before returning
> > to the page allocator.  Otherwise, it can stay frozen indefinitely and
> > no memory will be freed.
> 
> OK, I can see the race now:
> oom_kill_task				refrigerator
>   set_tsk_thread_flag(p, TIF_MEMDIE);
>   force_sig(SIGKILL, p);
>   if (frozen(p))
>   	thaw_process(p)
> 					  frozen_process();
> 					  [...]
> 					  if (!frozen(current))
> 					  	break;
> 					  schedule();
> 
> select_bad_process
>   [...]
>   if (test_tsk_thread_flag(p, TIF_MEMDIE))
> 	  return ERR_PTR(-1UL);
> 
> So we either have to make sure that TIF_MEMDIE task is not frozen in
> select_bad_process (your patch) or check for fatal_signal_pending
> in refrigerator before we schedule and break out of the loop. Maybe the
> later one is safer? Rafael?

What about this?
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