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Tue, 17 Dec 2019 08:45:09 -0800 (PST) Subject: Re: [PATCH 3/3] io_uring: move *queue_link_head() from common path To: Pavel Begunkov , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <17f7900c-385f-0dfa-11bf-af99d080f894@gmail.com> From: Jens Axboe Message-ID: <76917820-052d-9597-133d-424fee3edade@kernel.dk> Date: Tue, 17 Dec 2019 09:45:08 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <17f7900c-385f-0dfa-11bf-af99d080f894@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 12/16/19 4:38 PM, Pavel Begunkov wrote: > On 17/12/2019 02:22, Pavel Begunkov wrote: >> Move io_queue_link_head() to links handling code in io_submit_sqe(), >> so it wouldn't need extra checks and would have better data locality. >> >> Signed-off-by: Pavel Begunkov >> --- >> fs/io_uring.c | 32 ++++++++++++++------------------ >> 1 file changed, 14 insertions(+), 18 deletions(-) >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index bac9e711e38d..a880ed1409cb 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -3373,13 +3373,15 @@ static bool io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state, >> struct io_kiocb **link) >> { >> struct io_ring_ctx *ctx = req->ctx; >> + unsigned int sqe_flags; >> int ret; >> >> + sqe_flags = READ_ONCE(req->sqe->flags); >> req->user_data = READ_ONCE(req->sqe->user_data); >> trace_io_uring_submit_sqe(ctx, req->user_data, true, req->in_async); >> >> /* enforce forwards compatibility on users */ >> - if (unlikely(req->sqe->flags & ~SQE_VALID_FLAGS)) { >> + if (unlikely(sqe_flags & ~SQE_VALID_FLAGS)) { >> ret = -EINVAL; >> goto err_req; >> } >> @@ -3402,10 +3404,10 @@ static bool io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state, >> if (*link) { >> struct io_kiocb *head = *link; >> >> - if (req->sqe->flags & IOSQE_IO_DRAIN) >> + if (sqe_flags & IOSQE_IO_DRAIN) >> head->flags |= REQ_F_DRAIN_LINK | REQ_F_IO_DRAIN; >> >> - if (req->sqe->flags & IOSQE_IO_HARDLINK) >> + if (sqe_flags & IOSQE_IO_HARDLINK) >> req->flags |= REQ_F_HARDLINK; >> >> if (io_alloc_async_ctx(req)) { >> @@ -3421,9 +3423,15 @@ static bool io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state, >> } >> trace_io_uring_link(ctx, req, head); >> list_add_tail(&req->link_list, &head->link_list); >> - } else if (req->sqe->flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) { >> + >> + /* last request of a link, enqueue the link */ >> + if (!(sqe_flags & IOSQE_IO_LINK)) { > > This looks suspicious (as well as in the current revision). Returning back > to my questions a few days ago can sqe->flags have IOSQE_IO_HARDLINK, but not > IOSQE_IO_LINK? I don't find any check. > > In other words, should it be as follows? > !(sqe_flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) Yeah, I think that should check for both. I'm fine with either approach in general: - IOSQE_IO_HARDLINK must have IOSQE_IO_LINK set or - IOSQE_IO_HARDLINK implies IOSQE_IO_LINK Seems like the former is easier to verify in terms of functionality, since we can rest easy if we check this early and -EINVAL if that isn't the case. What do you think? -- Jens Axboe