Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 7 Jan 2019 14:52:15 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Qian Cai <cai@lca.pw>
Cc:     Ingo Molnar <mingo@redhat.com>,
        linux kernel <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>, gkohli@codeaurora.org
Subject: Re: kernel BUG at kernel/sched/core.c:3490!
Message-ID: <20190107135215.GG14122@hirez.programming.kicks-ass.net>
References: <ba9c5ad8-d78c-904d-0430-a67d8e3ea729@lca.pw>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <ba9c5ad8-d78c-904d-0430-a67d8e3ea729@lca.pw>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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?