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Subject: Re: [PATCH] block: fix a crash in do_task_dead()
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Jens Axboe <axboe@kernel.dk>, Qian Cai <cai@lca.pw>,
        akpm@linux-foundation.org, hch@lst.de, mingo@redhat.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
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From:   Gaurav Kohli <gkohli@codeaurora.org>
Message-ID: <154008a8-9d29-2411-28a0-0284a95b4481@codeaurora.org>
Date:   Tue, 11 Jun 2019 10:09:06 +0530
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>>> +
>>
>> Hi Peter, Jen,
>>
>> As we are not taking pi_lock here , is there possibility of same task dead
>> call comes as this point of time for current thread, bcoz of which we have
>> seen earlier issue after this commit 0619317ff8ba
>> [T114538]  do_task_dead+0xf0/0xf8
>> [T114538]  do_exit+0xd5c/0x10fc
>> [T114538]  do_group_exit+0xf4/0x110
>> [T114538]  get_signal+0x280/0xdd8
>> [T114538]  do_notify_resume+0x720/0x968
>> [T114538]  work_pending+0x8/0x10
>>
>> Is there a chance of TASK_DEAD set at this point of time?
> 
> In this case try_to_wake_up(current, TASK_NORMAL) will do nothing, see the
> if (!(p->state & state)) above.
> 
> See also the comment about set_special_state() above. It disables irqs and
> this is enough to ensure that try_to_wake_up(current) from irq can't race
> with set_special_state(TASK_DEAD).

Thanks Oleg,

I missed that part(both thread and interrupt is in same core only), So 
that situation would never come.
> 
> Oleg.
> 

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