On Thu, Nov 18, 2021 at 09:06:27AM +0100, Peter Zijlstra wrote: > On Wed, Nov 17, 2021 at 03:50:17PM -0800, Linus Torvalds wrote: > > > I really don't think the WCHAN code should use unwinders at all. It's > > too damn fragile, and it's too easily triggered from user space. > > On x86, esp. with ORC, it pretty much has to. The thing is, the ORC > unwinder has been very stable so far. I'm guessing there's some really > stupid thing going on, like for example trying to unwind a freed stack. > > I *just* managed to reproduce, so let me go have a poke. Confirmed, with the below it no longer reproduces. Now, let me go undo that and fix the unwinder to not explode while trying to unwind nothing. --- diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 862af1db22ab..f810c5192cb9 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1978,7 +1978,7 @@ unsigned long get_wchan(struct task_struct *p) raw_spin_lock_irq(&p->pi_lock); state = READ_ONCE(p->__state); smp_rmb(); /* see try_to_wake_up() */ - if (state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq) + if (state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq && !(p->flags & PF_EXITING)) ip = __get_wchan(p); raw_spin_unlock_irq(&p->pi_lock);
