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Subject: Re: kernel BUG at kernel/sched/core.c:3490!
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        linux kernel <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>, gkohli@codeaurora.org
References: <ba9c5ad8-d78c-904d-0430-a67d8e3ea729@lca.pw>
 <20190107135215.GG14122@hirez.programming.kicks-ass.net>
From:   Qian Cai <cai@lca.pw>
Message-ID: <46089f1c-ad72-c96c-2f35-c2f60e726462@lca.pw>
Date:   Mon, 7 Jan 2019 09:36:05 -0500
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On 1/7/19 8:52 AM, Peter Zijlstra wrote:
> 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?

Running LTP oom01 [1] triggered it at least once in five attempts every time so
far on v4.20+. Have not tried much on v5.0-rc1 yet.

[1]
https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/oom/oom01.c