On 04/16, Oleg Nesterov wrote:
>
> On 04/16, Satoru Takeuchi wrote:
> >
> > --- linux-2.6.21-rc6-mm1.tsfix.orig/kernel/exit.c 2007-04-15
> > 16:56:12.000000000 +0900
> > +++ linux-2.6.21-rc6-mm1.tsfix/kernel/exit.c 2007-04-15
> > 16:56:17.000000000 +0900
> > @@ -680,10 +680,14 @@
> > reaper = child_reaper(father);
> > break;
> > }
> > + if (reaper->time_slice_reaper == father)
> > + reaper->time_slice_reaper = NULL;
> > } while (reaper->exit_state);
> >
> > list_for_each_safe(_p, _n, &father->children) {
> > p = list_entry(_p, struct task_struct, sibling);
> > + if (p->time_slice_reaper == father)
> > + p->time_slice_reaper = NULL;
> > choose_new_parent(p, reaper);
> > reparent_thread(p, father);
> > }
> > Index: linux-2.6.21-rc6-mm1.tsfix/kernel/sched.c
> > ===================================================================
> > --- linux-2.6.21-rc6-mm1.tsfix.orig/kernel/sched.c 2007-04-15
> > 16:56:12.000000000 +0900
> > +++ linux-2.6.21-rc6-mm1.tsfix/kernel/sched.c 2007-04-15
> > 16:56:17.000000000 +0900
> > @@ -1693,7 +1693,7 @@
> > * The remainder of the first timeslice might be recovered by
> > * the parent if the child exits early enough.
> > */
> > - p->first_time_slice = 1;
> > + p->time_slice_reaper = current;
> > p->timestamp = sched_clock();
> > local_irq_enable();
>
> I am afraid this doesn't work for CLONE_THREAD. Suppose that some sub-thread
> (not
> main thread) T1 creates another sub-thread, T2.
>
> T2->time_slice_reaper = T1.
>
> then T1 exits, but forget_original_parent(T1) doesn't change
> T2->time_slice_reaper,
> because T2 is not on T1->children list. Now T2->time_slice_reaper points to an
> already freed task_struct.
In case I was not clear...
Note that "do {} while ()" loop in forget_original_parent() stops when it finds
a sub-thread with ->exit_state == 0. This means we can miss another sub-thread
which has ->time_slice_reaper == father.
To make this correct, we should iterate over all thread-group, but this can slow
down exit() when we have a lot of threads.
I guess we need Ingo's opinion on that.
Oleg.
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