Commit f09c8643 authored by Hao Xu's avatar Hao Xu Committed by Jens Axboe
Browse files

io_uring: kbuf: add comments for some tricky code 



Add comments to explain why it is always under uring lock when
incrementing head in __io_kbuf_recycle. And rectify one comemnt about
kbuf consuming in iowq case.

Signed-off-by: default avatarHao Xu <howeyxu@tencent.com>
Link: https://lore.kernel.org/r/20220617050429.94293-1-hao.xu@linux.dev


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9ca9fb24

io_uring/kbuf.c

+14 −6
Original line number Diff line number Diff line
@@ -52,6 +52,13 @@ void __io_kbuf_recycle(struct io_kiocb *req, unsigned issue_flags) 
	if (req->flags & REQ_F_BUFFER_RING) {

		if (req->buf_list) {

			if (req->flags & REQ_F_PARTIAL_IO) {

				/*

				 * If we end up here, then the io_uring_lock has

				 * been kept held since we retrieved the buffer.

				 * For the io-wq case, we already cleared

				 * req->buf_list when the buffer was retrieved,

				 * hence it cannot be set here for that case.

				 */

				req->buf_list->head++;

				req->buf_list = NULL;

			} else {
@@ -163,12 +170,13 @@ static void __user *io_ring_buffer_select(struct io_kiocb *req, size_t *len, 
	if (issue_flags & IO_URING_F_UNLOCKED || !file_can_poll(req->file)) {

		/*

		 * If we came in unlocked, we have no choice but to consume the

		 * buffer here. This does mean it'll be pinned until the IO

		 * completes. But coming in unlocked means we're in io-wq

		 * context, hence there should be no further retry. For the

		 * locked case, the caller must ensure to call the commit when

		 * the transfer completes (or if we get -EAGAIN and must poll

		 * or retry).

		 * buffer here, otherwise nothing ensures that the buffer won't

		 * get used by others. This does mean it'll be pinned until the

		 * IO completes, coming in unlocked means we're being called from

		 * io-wq context and there may be further retries in async hybrid

		 * mode. For the locked case, the caller must call commit when

		 * the transfer completes (or if we get -EAGAIN and must poll of

		 * retry).

		 */

		req->buf_list = NULL;

		bl->head++;