On 02 Aug 2014, at 11:19, Oleg Nesterov <o...@redhat.com> wrote:
> On 07/31, Aleksei Besogonov wrote:
>>
>> On 31 Jul 2014, at 00:43, David Rientjes <rient...@google.com> wrote:
>>
>>> The while_each_thread() in vm_is_stack() looks suspicious since the task
>>> isn't current and rcu won't protect the iteration, and we also don't hold
>>> sighand lock or a readlock on tasklist_lock.
>>> I think Oleg will know how to proceed, cc'd.
>> I’m attaching a minimal test case that can reproduce the issue. Works in
>> 100% cases on any system I’ve tried.
> Thanks. I think David is right and we need the simple patch below.
> This reminds me I should kill while_each_thread :/
> Any chance you can test it? If not, I will do this later and send
> the patch if it helps.
Thanks, it works on the rc7 kernel.
I can make a backported version for earlier kernels if nobody else is
interested.
>
> Oleg.
>
> --- x/mm/util.c
> +++ x/mm/util.c
> @@ -277,17 +277,14 @@ pid_t vm_is_stack(struct task_struct *ta
>
> if (in_group) {
> struct task_struct *t;
> - rcu_read_lock();
> - if (!pid_alive(task))
> - goto done;
>
> - t = task;
> - do {
> + rcu_read_lock();
> + for_each_thread(task, t) {
> if (vm_is_stack_for_task(t, vma)) {
> ret = t->pid;
> goto done;
> }
> - } while_each_thread(task, t);
> + }
> done:
> rcu_read_unlock();
> }
>
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