Re: [PATCH] psi: get poll_work to run when calling poll syscall next time

[Jason Xing <kerneljasonxing@linux.alibaba.com>]

Hello,

Could someone take a quick look at this patch? It's not complicated at 
all, just one line added into PSI which can make the poll() run in the 
right way.

Thanks,
Jason

On 2019/7/23 下午2:45, 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>
> ---
>   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);
>   }
>