On 3/29/24 9:50 AM, Pavel Begunkov wrote:
> On 3/29/24 13:31, Jens Axboe wrote:
>> On 3/29/24 6:51 AM, Pavel Begunkov wrote:
>>> On 3/28/24 18:52, Jens Axboe wrote:
>>>> All our task_work handling is targeted at the state in the io_kiocb
>>>> itself, which is what it is being used for. However, MSG_RING rolls its
>>>> own task_work handling, ignoring how that is usually done.
>>>>
>>>> In preparation for switching MSG_RING to be able to use the normal
>>>> task_work handling, add io_req_task_work_add_remote() which allows the
>>>> caller to pass in the target io_ring_ctx and task.
>>>>
>>>> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>>>> ---
>>>> io_uring/io_uring.c | 27 +++++++++++++++++++--------
>>>> io_uring/io_uring.h | 2 ++
>>>> 2 files changed, 21 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>>>> index 9978dbe00027..609ff9ea5930 100644
>>>> --- a/io_uring/io_uring.c
>>>> +++ b/io_uring/io_uring.c
>>>> @@ -1241,9 +1241,10 @@ void tctx_task_work(struct callback_head *cb)
>>>> WARN_ON_ONCE(ret);
>>>> }
>>>> -static inline void io_req_local_work_add(struct io_kiocb *req, unsigned tw_flags)
>>>> +static inline void io_req_local_work_add(struct io_kiocb *req,
>>>> + struct io_ring_ctx *ctx,
>>>> + unsigned tw_flags)
>>>> {
>>>> - struct io_ring_ctx *ctx = req->ctx;
>>>> unsigned nr_wait, nr_tw, nr_tw_prev;
>>>> unsigned long flags;
>>>> @@ -1291,9 +1292,10 @@ static inline void io_req_local_work_add(struct io_kiocb *req, unsigned tw_flags
>>>> wake_up_state(ctx->submitter_task, TASK_INTERRUPTIBLE);
>>>> }
>>>> -static void io_req_normal_work_add(struct io_kiocb *req)
>>>> +static void io_req_normal_work_add(struct io_kiocb *req,
>>>> + struct task_struct *task)
>>>> {
>>>> - struct io_uring_task *tctx = req->task->io_uring;
>>>> + struct io_uring_task *tctx = task->io_uring;
>>>> struct io_ring_ctx *ctx = req->ctx;
>>>> unsigned long flags;
>>>> bool was_empty;
>>>> @@ -1319,7 +1321,7 @@ static void io_req_normal_work_add(struct io_kiocb *req)
>>>> return;
>>>> }
>>>> - if (likely(!task_work_add(req->task, &tctx->task_work, ctx->notify_method)))
>>>> + if (likely(!task_work_add(task, &tctx->task_work, ctx->notify_method)))
>>>> return;
>>>> io_fallback_tw(tctx, false);
>>>> @@ -1328,9 +1330,18 @@ static void io_req_normal_work_add(struct io_kiocb *req)
>>>> void __io_req_task_work_add(struct io_kiocb *req, unsigned flags)
>>>> {
>>>> if (req->ctx->flags & IORING_SETUP_DEFER_TASKRUN)
>>>> - io_req_local_work_add(req, flags);
>>>> + io_req_local_work_add(req, req->ctx, flags);
>>>> + else
>>>> + io_req_normal_work_add(req, req->task);
>>>> +}
>>>> +
>>>> +void io_req_task_work_add_remote(struct io_kiocb *req, struct task_struct *task,
>>>> + struct io_ring_ctx *ctx, unsigned flags)
>>>
>>> Urgh, even the declration screams that there is something wrong
>>> considering it _either_ targets @ctx or @task.
>>>
>>> Just pass @ctx, so it either use ctx->submitter_task or
>>> req->task, hmm?
>>
>> I actually since changed the above to use a common helper, so was
>> scratching my head a bit over your comment as it can't really work in
>> that setup without needing to check for whether ->submitter_task is set
>> or not. But I do agree this would be nicer, so I'll just return to using
>> the separate helpers for this and it should fall out nicely. The only
>> odd caller is the MSG_RING side, so makes sense to have it a bit more
>> separate rather than try and fold it in with the regular side of using
>> task_work.
>>
>>> A side note, it's a dangerous game, I told it before. At least
>>> it would've been nice to abuse lockdep in a form of:
>>>
>>> io_req_task_complete(req, tw, ctx) {
>>> lockdep_assert(req->ctx == ctx);
>>> ...
>>> }
>>>
>>> but we don't have @ctx there, maybe we'll add it to tw later.
>>
>> Agree, but a separate thing imho.
>
> It's not in a sense that condition couldn't have happened
> before and the patch opening all possibilities.
>
> We actually have @ctx via struct io_tctx_node, so considering
> fallback it would probably be:
>
> lockdep_assert(!current->io_uring ||
> current->io_uring->ctx == req->ctx);
That's not a bad idea. I did run all the testing verifying the ctx, and
it all appears fine. But adding the check is a good idea in general.
Want to send it?
--
Jens Axboe
