From: Thomas Gleixner <tglx@linutronix.de>
To: Jens Axboe <axboe@kernel.dk>
Cc: "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] task_work: cleanup notification modes
Date: Sat, 17 Oct 2020 01:38:58 +0200 [thread overview]
Message-ID: <87wnzpivvx.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <2ebe7e45-b4e5-1a6b-d3ee-4a790817a119@kernel.dk>
On Fri, Oct 16 2020 at 17:13, Jens Axboe wrote:
> /**
> * task_work_add - ask the @task to execute @work->func()
> * @task: the task which should run the callback
> * @work: the callback to run
> * @notify: how to notify the targeted task
> *
> * Queue @work for task_work_run() below and notify the @task if @notify
> * is @TWA_RESUME or @TWA_SIGNAL. @TWA_SIGNAL work like signals, in that the
s/the//
> * it will interrupt the targeted task and run the task_work. @TWA_RESUME
> * work is run only when the task exits the kernel and returns to user mode.
> * Fails if the @task is exiting/exited and thus it can't process this @work.
> * Otherwise @work->func() will be called when the @task returns from kernel
> * mode or exits.
Yes, that makes a lot more sense.
What's still lacking is a description of the return value and how to act
upon it.
Most of the call sites ignore it, some are acting upon it but I can't
make any sense of these actions:
fs/io_uring.c- notify = 0;
fs/io_uring.c- if (!(ctx->flags & IORING_SETUP_SQPOLL) && twa_signal_ok)
fs/io_uring.c- notify = TWA_SIGNAL;
fs/io_uring.c-
fs/io_uring.c: ret = task_work_add(tsk, &req->task_work, notify);
fs/io_uring.c- if (!ret)
fs/io_uring.c- wake_up_process(tsk);
???
fs/io_uring.c- if (unlikely(ret)) {
fs/io_uring.c- struct task_struct *tsk;
fs/io_uring.c-
fs/io_uring.c- init_task_work(&req->task_work, io_req_task_cancel);
fs/io_uring.c- tsk = io_wq_get_task(req->ctx->io_wq);
fs/io_uring.c: task_work_add(tsk, &req->task_work, 0);
fs/io_uring.c- wake_up_process(tsk);
yet more magic wakeup.
fs/io_uring.c-
fs/io_uring.c- init_task_work(&req->task_work, io_req_task_submit);
fs/io_uring.c- percpu_ref_get(&req->ctx->refs);
fs/io_uring.c-
fs/io_uring.c- /* submit ref gets dropped, acquire a new one */
fs/io_uring.c- refcount_inc(&req->refs);
fs/io_uring.c: ret = io_req_task_work_add(req, true);
fs/io_uring.c- if (unlikely(ret)) {
fs/io_uring.c- struct task_struct *tsk;
fs/io_uring.c-
fs/io_uring.c- /* queue just for cancelation */
fs/io_uring.c- init_task_work(&req->task_work, io_req_task_cancel);
fs/io_uring.c- tsk = io_wq_get_task(req->ctx->io_wq);
fs/io_uring.c: task_work_add(tsk, &req->task_work, 0);
fs/io_uring.c- wake_up_process(tsk);
Ditto. Why the heck is this wakeup making any sense? The initial
task_work_add() within io_req_task_work_add() failed already ...
fs/io_uring.c: ret = io_req_task_work_add(req, twa_signal_ok);
fs/io_uring.c- if (unlikely(ret)) {
fs/io_uring.c- struct task_struct *tsk;
fs/io_uring.c-
fs/io_uring.c- WRITE_ONCE(poll->canceled, true);
fs/io_uring.c- tsk = io_wq_get_task(req->ctx->io_wq);
fs/io_uring.c: task_work_add(tsk, &req->task_work, 0);
fs/io_uring.c- wake_up_process(tsk);
...
Thanks,
tglx
next prev parent reply other threads:[~2020-10-16 23:39 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-16 15:16 [PATCH] task_work: cleanup notification modes Jens Axboe
2020-10-16 21:44 ` Thomas Gleixner
2020-10-16 22:39 ` Jens Axboe
2020-10-16 23:09 ` Thomas Gleixner
2020-10-16 23:13 ` Jens Axboe
2020-10-16 23:38 ` Thomas Gleixner [this message]
2020-10-16 23:43 ` Jens Axboe
2020-10-17 15:31 ` Thomas Gleixner
2020-10-17 15:36 ` Jens Axboe
2020-10-17 20:18 ` Thomas Gleixner
2020-10-17 20:32 ` Jens Axboe
2020-10-17 21:01 ` Thomas Gleixner
2020-10-17 21:03 ` Jens Axboe
2020-10-17 21:17 ` Thomas Gleixner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87wnzpivvx.fsf@nanos.tec.linutronix.de \
--to=tglx@linutronix.de \
--cc=axboe@kernel.dk \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).