linux-kernel - Re: [PATCH v3 0/4] forbid fix {SQ,IO}POLL

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Message-ID: <cc3197f9-e8b1-ac13-c121-291bb32646e3@kernel.dk>
Date:   Thu, 4 Jun 2020 13:52:10 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/4] forbid fix {SQ,IO}POLL

On 6/4/20 1:22 PM, Pavel Begunkov wrote:
> On 04/06/2020 20:06, Jens Axboe wrote:
>> On 6/3/20 12:51 PM, Jens Axboe wrote:
>>> On 6/3/20 9:03 AM, Pavel Begunkov wrote:
>>>> The first one adds checks {SQPOLL,IOPOLL}. IOPOLL check can be
>>>> moved in the common path later, or rethinked entirely, e.g.
>>>> not io_iopoll_req_issued()'ed for unsupported opcodes.
>>>>
>>>> 3 others are just cleanups on top.
>>>>
>>>>
>>>> v2: add IOPOLL to the whole bunch of opcodes in [1/4].
>>>>     dirty and effective.
>>>> v3: sent wrong set in v2, re-sending right one 
>>>>
>>>> Pavel Begunkov (4):
>>>>   io_uring: fix {SQ,IO}POLL with unsupported opcodes
>>>>   io_uring: do build_open_how() only once
>>>>   io_uring: deduplicate io_openat{,2}_prep()
>>>>   io_uring: move send/recv IOPOLL check into prep
>>>>
>>>>  fs/io_uring.c | 94 ++++++++++++++++++++++++++-------------------------
>>>>  1 file changed, 48 insertions(+), 46 deletions(-)
>>>
>>> Thanks, applied.
>>
>> #1 goes too far, provide/remove buffers is fine with iopoll. I'll
>> going to edit the patch.
> 
> Conceptually it should work, but from a quick look:
> 
> - io_provide_buffers() drops a ref from req->refs, which should've
> been used by iopoll*. E.g. io_complete_rw_iopoll() doesn't do that.
> 
> - it doesn't set REQ_F_IOPOLL_COMPLETED, thus iopoll* side will
> call req->file->iopoll().

We don't poll for provide/remove buffers, or file update. The
completion is done inline. The REQ_F_IOPOLL_COMPLETED and friends
is only applicable on read/writes.

-- 
Jens Axboe