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Date:   Tue, 23 Jul 2019 18:02:09 +0800
From:   Caspar Zhang <caspar@casparzhang.com>
To:     Jason Xing <kerneljasonxing@linux.alibaba.com>
Cc:     hannes@cmpxchg.org, surenb@google.com, mingo@redhat.com,
        peterz@infradead.org, dennis@kernel.org, axboe@kernel.dk,
        lizefan@huawei.com, tj@kernel.org, linux-kernel@vger.kernel.org,
        caspar@linux.alibaba.com, joseph.qi@linux.alibaba.com
Subject: Re: [PATCH] psi: get poll_work to run when calling poll syscall next
 time
Message-ID: <20190723100209.GA78446@casparzhang.com>
References: <1563864339-2621-1-git-send-email-kerneljasonxing@linux.alibaba.com>
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On Tue, Jul 23, 2019 at 02:45:39PM +0800, Jason Xing wrote:
> Only when calling the poll syscall the first time can user
> receive POLLPRI correctly. After that, user always fails to
> acquire the event signal.
>
> Reproduce case:
> 1. Get the monitor code in Documentation/accounting/psi.txt
> 2. Run it, and wait for the event triggered.
> 3. Kill and restart the process.
>
> If the user doesn't kill the monitor process, it seems the
> poll_work works fine. After killing and restarting the monitor,
> the poll_work in kernel will never run again due to the wrong
> value of poll_scheduled. Therefore, we should reset the value
> as group_init() does after the last trigger is destroyed.
>
> Signed-off-by: Jason Xing <kerneljasonxing@linux.alibaba.com>

Reviewed-by: Caspar Zhang <caspar@linux.alibaba.com>

> ---
>  kernel/sched/psi.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 7acc632..66f4385 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -1133,6 +1133,12 @@ static void psi_trigger_destroy(struct kref *ref)
>  	if (kworker_to_destroy) {
>  		kthread_cancel_delayed_work_sync(&group->poll_work);
>  		kthread_destroy_worker(kworker_to_destroy);
> +		/*
> +		 * The poll_work should have the chance to be put into the
> +		 * kthread queue when calling poll syscall next time. So
> +		 * reset poll_scheduled to zero as group_init() does
> +		 */
> +		atomic_set(&group->poll_scheduled, 0);
>  	}
>  	kfree(t);
>  }
> --
> 1.8.3.1
>

--
        Thanks,
        Caspar