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SubjectRe: [PATCH 3/3] io_uring: move *queue_link_head() from common path
> On Tue, Dec 17, 2019 at 02:22:09AM +0300, 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.
>
> ---
> 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);

Just out of curiosity, why READ_ONCE it necessary here? I though, that
since io_submit_sqes happens within a uring_lock, it's already
protected. Do I miss something?

> @@ -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)) {

Yes, as you mentioned in the previous email, it seems correct that if
IOSQE_IO_HARDLINK imply IOSQE_IO_LINK, then here we need to check both.

> + io_queue_link_head(head);
> + *link = NULL;
> + }
> + } else if (sqe_flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) {

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