linux-kernel - Re: kernel BUG at kernel/sched/core.c:3490!

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Date:   Mon, 7 Jan 2019 14:52:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Qian Cai <cai@....pw>
Cc:     Ingo Molnar <mingo@...hat.com>,
        linux kernel <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>, gkohli@...eaurora.org
Subject: Re: kernel BUG at kernel/sched/core.c:3490!

On Tue, Jan 01, 2019 at 12:44:35AM -0500, Qian Cai wrote:
> Running some mmap() workloads to put the system on low memory situation with
> swapping and OOM, and then it trigger this BUG(),
> 
> void __noreturn do_task_dead(void)
> {
>         /* Causes final put_task_struct in finish_task_switch(): */
>         set_special_state(TASK_DEAD);
> 
>         /* Tell freezer to ignore us: */
>         current->flags |= PF_NOFREEZE;
> 
>         __schedule(false);
>         BUG();
> 
>         /* Avoid "noreturn function does return" - but don't continue if BUG()
> is a NOP: */
>         for (;;)
>                 cpu_relax();
> }

This would mean that we somehow loose the TASK_DEAD state before hitting
schedule(), but that is something that should be avoided by
set_special_state(), which is supposed to serialize against concurrent
wake-ups.

Also see commit: b5bf9a90bbeb ("sched/core: Introduce set_special_state()")

How readily does this reproduce?