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.
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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