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
