On Tue, Jun 28, 2016 at 1:12 PM, Oleg Nesterov <o...@redhat.com> wrote: > On 06/28, Andy Lutomirski wrote: >> >> On Tue, Jun 28, 2016 at 11:58 AM, Oleg Nesterov <o...@redhat.com> wrote: >> > >> > Then how (say) proc_pid_stack() can work? If it hits the task which is >> > alreay dead we are (probably) fine, valid_stack_ptr() should fail iiuc. >> > >> > But what if we race with the last schedule() ? "addr = *stack" can read >> > the already vfree'ed memory, no? >> > >> > Looks like print_context_stack/etc need probe_kernel_address or I missed >> > something. >> >> Yuck. I suppose I could add a reference count to protect the stack. >> Would that simplify the kthread code? > > Well yes, that is why I asked. So please tell me if you are going to > do this... > > But we can fix kthread code without this hack which we do not need in > the long term anyway. Unfortunaly we need to cleanup kernel/smpboot.c > first. And I was going to do this a long ago for quite different reason ;) > > So please forget unless you see another reason for this change. >
But I might need to that anyway for procfs to read the the stack, right? Do you see another way to handle that case? I'm thinking of adding: void *try_get_task_stack(struct task_struct *tsk); void put_task_stack(struct task_struct *tsk); where try_get_task_stack can return NULL. --Andy
