Re: 5.8-rc*: kernel BUG at kernel/signal.c:1917

[Oleg Nesterov <oleg@redhat.com>]

On 07/20, Peter Zijlstra wrote:
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4193,9 +4193,6 @@ static void __sched notrace __schedule(bool preempt)
>  	local_irq_disable();
>  	rcu_note_context_switch(preempt);
>  
> -	/* See deactivate_task() below. */
> -	prev_state = prev->state;
> -
>  	/*
>  	 * Make sure that signal_pending_state()->signal_pending() below
>  	 * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
> @@ -4223,7 +4220,8 @@ static void __sched notrace __schedule(bool preempt)
>  	 * We must re-load prev->state in case ttwu_remote() changed it
>  	 * before we acquired rq->lock.
>  	 */
> -	if (!preempt && prev_state && prev_state == prev->state) {
> +	prev_state = prev->state;
> +	if (!preempt && prev_state) {

Heh ;) Peter, you know what? I did the same change and tried to understand
why it is wrong and what have I missed.

Thanks, now I can relax. But my head hurts too, I'll probably try to re-read
this code and other emails from you tomorrow.

Oleg.