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io_uring: kbuf: add comments for some tricky code

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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: Hao Xu <howeyxu@tencent.com>
Link: https://lore.kernel.org/r/20220617050429.94293-1-hao.xu@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Hao Xu 2022-06-17 13:04:29 +08:00 committed by Jens Axboe
parent 9ca9fb24d5
commit f09c8643f0
1 changed files with 14 additions and 6 deletions
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20
io_uring/kbuf.c
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@ -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++;