Re: [PATCH -mm] scheduler: fix the return of the first time_slice

From: Oleg Nesterov
Date: Mon Apr 16 2007 - 06:46:53 EST


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.

Oleg.

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