From: Pavel Begunkov <asml.silence@gmail.com> mainline inclusion from mainline-5.6-rc1 commit 8cdf2193a3335b4cfb6e023b41ac293d0843d287 category: feature bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27 CVE: NA --------------------------- Draining the middle of a link is tricky, so leave a comment there Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: yangerkun <yangerkun@huawei.com> Reviewed-by: zhangyi (F) <yi.zhang@huawei.com> Signed-off-by: Cheng Jian <cj.chengjian@huawei.com> --- fs/io_uring.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/io_uring.c b/fs/io_uring.c index 58a204cb5337..14ca1fadd7b5 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -4571,6 +4571,13 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe, if (*link) { struct io_kiocb *head = *link; + /* + * Taking sequential execution of a link, draining both sides + * of the link also fullfils IOSQE_IO_DRAIN semantics for all + * requests in the link. So, it drains the head and the + * next after the link request. The last one is done via + * drain_next flag to persist the effect across calls. + */ if (sqe_flags & IOSQE_IO_DRAIN) { head->flags |= REQ_F_IO_DRAIN; ctx->drain_next = 1; -- 2.25.1