Messages in this thread |  | | From | Kirill Tkhai <> | Subject | Re: [PATCH v4] sched/numa: fix unsafe get_task_struct() in task_numa_assign() | Date | Mon, 10 Nov 2014 23:01:21 +0300 |
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10.11.2014, 19:45, "Sasha Levin" <sasha.levin@oracle.com>: > On 11/10/2014 11:36 AM, Kirill Tkhai wrote: >> I mean task_numa_find_cpu(). If a garbage is in cpumask_of_node(env->dst_nid) >> and cpu is bigger than mask, the check >> >> cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p) >> >> may be true. >> >> So, we dereference wrong rq in task_numa_compare(). It's not rq at all. >> Strange cpu may be from here. It's just a int number in a wrong memory. > > But the odds of the spinlock magic and owner pointer matching up are slim > to none in that case. The memory is also likely to be valid since KASAN didn't > complain about the access, so I don't believe it to be an access to freed memory.
I'm not good with lockdep checks, so I can't judge right now... Just a hypothesis.
>> A hypothesis that below may help: >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 826fdf3..a2b4a8a 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -1376,6 +1376,9 @@ static void task_numa_find_cpu(struct task_numa_env *env, >> { >> int cpu; >> >> + if (!node_online(env->dst_nid)) >> + return; > > I've changed that to BUG_ON(!node_online(env->dst_nid)) and will run it for a > bit.
I've looked one more time, and it looks like it's better to check for BUG_ON(env->dst_nid > MAX_NUMNODES). node_online() may do not work for insane nids.
Anyway, even if it's not connected, we need to initialize numa_preferred_nid of init_task, because it's inherited by kernel_init() (and /sbin/init too). I'll send the patch tomorrow.
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