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Date:   Thu, 20 Feb 2020 22:17:44 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     io-uring@vger.kernel.org, glauber@scylladb.com,
        asml.silence@gmail.com
Subject: Re: [PATCH 6/9] sched: add a sched_work list
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On Thu, Feb 20, 2020 at 01:31:48PM -0700, Jens Axboe wrote:
> This is similar to the task_works, and uses the same infrastructure, but
> the sched_work list is run when the task is being scheduled in or out.
> 
> The intended use case here is for core code to be able to add work
> that should be automatically run by the task, without the task needing
> to do anything. This is done outside of the task, one example would be
> from waitqueue handlers, or anything else that is invoked out-of-band
> from the task itself.
> 


> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 3445421266e7..ba62485d5b3d 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -3,7 +3,14 @@
>  #include <linux/task_work.h>
>  #include <linux/tracehook.h>
>  
> -static struct callback_head work_exited; /* all we need is ->next == NULL */
> +static void task_exit_func(struct callback_head *head)
> +{
> +}
> +
> +static struct callback_head work_exited = {
> +	.next	= NULL,
> +	.func	= task_exit_func,
> +};

Do we really need this? It seems to suggest we're trying to execute
work_exited, which would be an error.

Doing so would be the result of calling sched_work_run() after
exit_task_work(). I suppose that's actually possible.. the problem is
that that would reset sched_work to NULL and re-allow queueing works,
which would then leak.

I'll look at it in more detail tomorrow, I'm tired...