From: Oleg Nesterov <oleg@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-kernel@vger.kernel.org, io-uring@vger.kernel.org,
peterz@infradead.org, tglx@linutronix.de
Subject: Re: [PATCH 3/3] task_work: use TIF_TASKWORK if available
Date: Fri, 2 Oct 2020 17:14:16 +0200 [thread overview]
Message-ID: <20201002151415.GA29066@redhat.com> (raw)
In-Reply-To: <20201001194208.1153522-4-axboe@kernel.dk>
Heh. To be honest I don't really like 1-2 ;)
Unfortunately, I do not see a better approach right now. Let me think
until Monday, it is not that I think I will find a better solution, but
I'd like to try anyway.
Let me comment 3/3 for now.
On 10/01, Jens Axboe wrote:
>
> +static void task_work_signal(struct task_struct *task)
> +{
> +#ifndef TIF_TASKWORK
> + unsigned long flags;
> +
> + /*
> + * Only grab the sighand lock if we don't already have some
> + * task_work pending. This pairs with the smp_store_mb()
> + * in get_signal(), see comment there.
> + */
> + if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
> + lock_task_sighand(task, &flags)) {
> + task->jobctl |= JOBCTL_TASK_WORK;
> + signal_wake_up(task, 0);
> + unlock_task_sighand(task, &flags);
> + }
> +#else
> + set_tsk_thread_flag(task, TIF_TASKWORK);
> + set_notify_resume(task);
> +#endif
Again, I can't understand. task_work_signal(task) should set TIF_TASKWORK
to make signal_pending() = T _and_ wake/kick the target up, just like
signal_wake_up() does. Why do we set TIF_NOTIFY_RESUME ?
So I think that if we are going to add TIF_TASKWORK we should generalize
this logic and turn it into TIF_NOTIFY_SIGNAL. Similar to TIF_NOTIFY_RESUME
but implies signal_pending().
IOW, something like
void set_notify_signal(task)
{
if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_SIGNAL)) {
if (!wake_up_state(task, TASK_INTERRUPTIBLE))
kick_process(t);
}
}
// called by exit_to_user_mode_loop() if ti_work & _TIF_NOTIFY_SIGNAL
void tracehook_notify_signal(regs)
{
clear_thread_flag(TIF_NOTIFY_SIGNAL);
smp_mb__after_atomic();
if (unlikely(current->task_works))
task_work_run();
}
This way task_work_run() doesn't need to clear TIF_NOTIFY_SIGNAL and it can
have more users.
What do you think?
Oleg.
next prev parent reply other threads:[~2020-10-02 15:14 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 19:42 [PATCHSET RFC 0/3] kernel: decouple TASK_WORK TWA_SIGNAL handling from signals Jens Axboe
2020-10-01 19:42 ` [PATCH 1/3] kernel: add task_sigpending() helper Jens Axboe
2020-10-01 19:42 ` [PATCH 2/3] kernel: decouple TASK_WORK TWA_SIGNAL handling from signals Jens Axboe
2020-10-01 19:42 ` [PATCH 3/3] task_work: use TIF_TASKWORK if available Jens Axboe
2020-10-02 15:14 ` Oleg Nesterov [this message]
2020-10-02 15:31 ` Thomas Gleixner
2020-10-02 15:38 ` Oleg Nesterov
2020-10-02 16:18 ` Jens Axboe
2020-10-03 1:49 ` Thomas Gleixner
2020-10-03 15:35 ` Jens Axboe
2020-10-02 15:52 ` Jens Axboe
2020-10-02 16:42 ` Jens Axboe
2020-10-02 19:10 ` Thomas Gleixner
2020-10-02 20:14 ` Jens Axboe
2020-10-02 15:53 ` Jens Axboe
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