From: Jens Axboe <[email protected]>
To: Jann Horn <[email protected]>
Cc: io-uring <[email protected]>,
Glauber Costa <[email protected]>,
Peter Zijlstra <[email protected]>,
Pavel Begunkov <[email protected]>
Subject: Re: [PATCH 7/9] io_uring: add per-task callback handler
Date: Thu, 20 Feb 2020 14:56:21 -0800 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAG48ez3R3DWLry_aRAt47BQ05Y4Mr9yVXq49yuiRGNoyRMr3Lg@mail.gmail.com>
On 2/20/20 3:38 PM, Jann Horn wrote:
> On Thu, Feb 20, 2020 at 11:23 PM Jens Axboe <[email protected]> wrote:
>> On 2/20/20 3:14 PM, Jens Axboe wrote:
>>>>> @@ -3646,46 +3596,11 @@ static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
>>>>>
>>>>> list_del_init(&poll->wait.entry);
>>>>>
>>>> [...]
>>>>> + tsk = req->task;
>>>>> + req->result = mask;
>>>>> + init_task_work(&req->sched_work, io_poll_task_func);
>>>>> + sched_work_add(tsk, &req->sched_work);
>>>>
>>>> Doesn't this have to check the return value?
>>>
>>> Trying to think if we can get here with TASK_EXITING, but probably safer
>>> to just handle it in any case. I'll add that.
>>
>> Double checked this one, and I think it's good as-is, but needs a
>> comment. If the sched_work_add() fails, then the work item is still in
>> the poll hash on the ctx. That work is canceled on exit.
>
> You mean via io_poll_remove_all()? That doesn't happen when a thread
> dies, right?
Off of io_uring_flush, we do:
if (fatal_signal_pending(current) || (current->flags & PF_EXITING)) {
io_uring_cancel_task_poll(current);
io_uring_cancel_task_async(current);
io_wq_cancel_pid(ctx->io_wq, task_pid_vnr(current));
}
to cancel _anything_ that the task has pending.
> As far as I can tell, the following might happen:
>
> 1. process with threads A and B set up uring
> 2. thread B submits chained requests poll->read
> 3. thread A waits for request completion
> 4. thread B dies
> 5. poll waitqueue is notified, data is ready
Unless I'm mistaken, when B dies, the requests from #2 will be canceled.
> Even if there isn't a memory leak, you'd still want the read request
> to execute at some point so that thread A can see the result, right?
It just needs to complete, if the task is going away, then a cancelation
is fine too.
> And actually, in this scenario, wouldn't the req->task be a dangling
> pointer, since you're not holding a reference? Or is there some magic
> callback from do_exit() to io_uring that I missed? There is a comment
> "/* task will wait for requests on exit, don't need a ref */", but I
> don't see how that works...
That'd only be the case if we didn't cancel requests when it dies. I'll
double check if that's 100% the case.
--
Jens Axboe
next prev parent reply other threads:[~2020-02-20 22:56 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 20:31 [PATCHSET 0/9] io_uring: use polled async retry Jens Axboe
2020-02-20 20:31 ` [PATCH 1/9] io_uring: consider any io_read/write -EAGAIN as final Jens Axboe
2020-02-20 20:31 ` [PATCH 2/9] io_uring: io_accept() should hold on to submit reference on retry Jens Axboe
2020-02-20 20:31 ` [PATCH 3/9] sched: move io-wq/workqueue worker sched in/out into helpers Jens Axboe
2020-02-20 20:31 ` [PATCH 4/9] task_work_run: don't take ->pi_lock unconditionally Jens Axboe
2020-02-20 20:31 ` [PATCH 5/9] kernel: abstract out task work helpers Jens Axboe
2020-02-20 21:07 ` Peter Zijlstra
2020-02-20 21:08 ` Jens Axboe
2020-02-20 20:31 ` [PATCH 6/9] sched: add a sched_work list Jens Axboe
2020-02-20 21:17 ` Peter Zijlstra
2020-02-20 21:53 ` Jens Axboe
2020-02-20 22:02 ` Jens Axboe
2020-02-20 20:31 ` [PATCH 7/9] io_uring: add per-task callback handler Jens Axboe
2020-02-20 22:02 ` Jann Horn
2020-02-20 22:14 ` Jens Axboe
2020-02-20 22:18 ` Jens Axboe
2020-02-20 22:25 ` Jann Horn
2020-02-20 22:23 ` Jens Axboe
2020-02-20 22:38 ` Jann Horn
2020-02-20 22:56 ` Jens Axboe [this message]
2020-02-20 22:58 ` Jann Horn
2020-02-20 23:02 ` Jens Axboe
2020-02-20 22:23 ` Jann Horn
2020-02-20 23:00 ` Jens Axboe
2020-02-20 23:12 ` Jann Horn
2020-02-20 23:22 ` Jens Axboe
2020-02-21 1:29 ` Jann Horn
2020-02-21 17:32 ` Jens Axboe
2020-02-21 19:24 ` Jann Horn
2020-02-21 20:18 ` Jens Axboe
2020-02-20 22:56 ` Jann Horn
2020-02-21 10:47 ` Peter Zijlstra
2020-02-21 14:49 ` Jens Axboe
2020-02-21 15:02 ` Jann Horn
2020-02-21 16:12 ` Peter Zijlstra
2020-02-21 16:23 ` Peter Zijlstra
2020-02-21 20:13 ` Jens Axboe
2020-02-21 13:51 ` Pavel Begunkov
2020-02-21 14:50 ` Jens Axboe
2020-02-21 18:30 ` Pavel Begunkov
2020-02-21 19:10 ` Jens Axboe
2020-02-21 19:22 ` Pavel Begunkov
2020-02-23 6:00 ` Jens Axboe
2020-02-23 6:26 ` Jens Axboe
2020-02-23 11:02 ` Pavel Begunkov
2020-02-23 14:49 ` Jens Axboe
2020-02-23 14:58 ` Jens Axboe
2020-02-23 15:07 ` Jens Axboe
2020-02-23 18:04 ` Pavel Begunkov
2020-02-23 18:06 ` Jens Axboe
2020-02-23 17:55 ` Pavel Begunkov
2020-02-20 20:31 ` [PATCH 8/9] io_uring: mark requests that we can do poll async in io_op_defs Jens Axboe
2020-02-20 20:31 ` [PATCH 9/9] io_uring: use poll driven retry for files that support it Jens Axboe
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