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io_uring: return -EAGAIN to continue multishot 

Multishot errors can be mapped 1:1 to normal errors, but there are not
identical. It leads to a peculiar situation where all multishot requests
has to check in what context they're run and return different codes.

Unify them starting with EAGAIN / IOU_ISSUE_SKIP_COMPLETE(EIOCBQUEUED)
pair, which mean that core io_uring still owns the request and it should
be retried. In case of multishot it's naturally just continues to poll,
otherwise it might poll, use iowq or do any other kind of allowed
blocking. Introduce IOU_RETRY aliased to -EAGAIN for that.

Apart from obvious upsides, multishot can now also check for misuse of
IOU_ISSUE_SKIP_COMPLETE.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/da117b79ce72ecc3ab488c744e29fae9ba54e23b.1741453534.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
pull/1188/head
Pavel Begunkov 2025-03-08 17:19:32 +00:00 committed by Jens Axboe
parent 0396ad3766
commit 7a9dcb05f5
5 changed files with 29 additions and 44 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
io_uring/io_uring.c
View File

@ -1791,10 +1791,8 @@ int io_poll_issue(struct io_kiocb *req, io_tw_token_t tw)
ret = __io_issue_sqe(req, issue_flags, &io_issue_defs[req->opcode]);
WARN_ON_ONCE(ret == IOU_ISSUE_SKIP_COMPLETE);
WARN_ON_ONCE(ret == IOU_OK);
if (ret == IOU_ISSUE_SKIP_COMPLETE)
ret = 0;
return ret;
}

8
io_uring/io_uring.h
View File

@ -22,6 +22,14 @@ enum {
IOU_OK = 0,
IOU_ISSUE_SKIP_COMPLETE = -EIOCBQUEUED,
/*
* The request has more work to do and should be retried. io_uring will
* attempt to wait on the file for eligible opcodes, but otherwise
* it'll be handed to iowq for blocking execution. It works for normal
* requests as well as for the multi shot mode.
*/
IOU_RETRY = -EAGAIN,
/*
* Requeue the task_work to restart operations on this request. The
* actual value isn't important, should just be not an otherwise

47
io_uring/net.c
View File

@ -898,8 +898,7 @@ static inline bool io_recv_finish(struct io_kiocb *req, int *ret,
*/
if ((req->flags & REQ_F_APOLL_MULTISHOT) && !mshot_finished &&
io_req_post_cqe(req, *ret, cflags | IORING_CQE_F_MORE)) {
int mshot_retry_ret = IOU_ISSUE_SKIP_COMPLETE;
*ret = IOU_RETRY;
io_mshot_prep_retry(req, kmsg);
/* Known not-empty or unknown state, retry */
if (cflags & IORING_CQE_F_SOCK_NONEMPTY || kmsg->msg.msg_inq < 0) {
@ -907,12 +906,9 @@ static inline bool io_recv_finish(struct io_kiocb *req, int *ret,
return false;
/* mshot retries exceeded, force a requeue */
sr->nr_multishot_loops = 0;
mshot_retry_ret = IOU_REQUEUE;
if (issue_flags & IO_URING_F_MULTISHOT)
*ret = IOU_REQUEUE;
}
if (issue_flags & IO_URING_F_MULTISHOT)
*ret = mshot_retry_ret;
else
*ret = -EAGAIN;
return true;
}
@ -1070,16 +1066,15 @@ retry_multishot:
if (ret < min_ret) {
if (ret == -EAGAIN && force_nonblock) {
if (issue_flags & IO_URING_F_MULTISHOT) {
if (issue_flags & IO_URING_F_MULTISHOT)
io_kbuf_recycle(req, issue_flags);
return IOU_ISSUE_SKIP_COMPLETE;
}
return -EAGAIN;
return IOU_RETRY;
}
if (ret > 0 && io_net_retry(sock, flags)) {
sr->done_io += ret;
req->flags |= REQ_F_BL_NO_RECYCLE;
return -EAGAIN;
return IOU_RETRY;
}
if (ret == -ERESTARTSYS)
ret = -EINTR;
@ -1207,12 +1202,10 @@ retry_multishot:
ret = sock_recvmsg(sock, &kmsg->msg, flags);
if (ret < min_ret) {
if (ret == -EAGAIN && force_nonblock) {
if (issue_flags & IO_URING_F_MULTISHOT) {
if (issue_flags & IO_URING_F_MULTISHOT)
io_kbuf_recycle(req, issue_flags);
return IOU_ISSUE_SKIP_COMPLETE;
}
return -EAGAIN;
return IOU_RETRY;
}
if (ret > 0 && io_net_retry(sock, flags)) {
sr->len -= ret;
@ -1312,10 +1305,7 @@ int io_recvzc(struct io_kiocb *req, unsigned int issue_flags)
return IOU_STOP_MULTISHOT;
return IOU_OK;
}
if (issue_flags & IO_URING_F_MULTISHOT)
return IOU_ISSUE_SKIP_COMPLETE;
return -EAGAIN;
return IOU_RETRY;
}
void io_send_zc_cleanup(struct io_kiocb *req)
@ -1692,16 +1682,9 @@ retry:
put_unused_fd(fd);
ret = PTR_ERR(file);
if (ret == -EAGAIN && force_nonblock &&
!(accept->iou_flags & IORING_ACCEPT_DONTWAIT)) {
/*
* if it's multishot and polled, we don't need to
* return EAGAIN to arm the poll infra since it
* has already been done
*/
if (issue_flags & IO_URING_F_MULTISHOT)
return IOU_ISSUE_SKIP_COMPLETE;
return ret;
}
!(accept->iou_flags & IORING_ACCEPT_DONTWAIT))
return IOU_RETRY;
if (ret == -ERESTARTSYS)
ret = -EINTR;
} else if (!fixed) {
@ -1720,9 +1703,7 @@ retry:
io_req_post_cqe(req, ret, cflags | IORING_CQE_F_MORE)) {
if (cflags & IORING_CQE_F_SOCK_NONEMPTY || arg.is_empty == -1)
goto retry;
if (issue_flags & IO_URING_F_MULTISHOT)
return IOU_ISSUE_SKIP_COMPLETE;
return -EAGAIN;
return IOU_RETRY;
}
io_req_set_res(req, ret, cflags);

3
io_uring/poll.c
View File

@ -289,11 +289,12 @@ static int io_poll_check_events(struct io_kiocb *req, io_tw_token_t tw)
}
} else {
int ret = io_poll_issue(req, tw);
if (ret == IOU_STOP_MULTISHOT)
return IOU_POLL_REMOVE_POLL_USE_RES;
else if (ret == IOU_REQUEUE)
return IOU_POLL_REQUEUE;
if (ret < 0)
if (ret != IOU_RETRY && ret < 0)
return ret;
}

11
io_uring/rw.c
View File

@ -1068,9 +1068,7 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
*/
if (io_kbuf_recycle(req, issue_flags))
rw->len = 0;
if (issue_flags & IO_URING_F_MULTISHOT)
return IOU_ISSUE_SKIP_COMPLETE;
return -EAGAIN;
return IOU_RETRY;
} else if (ret <= 0) {
io_kbuf_recycle(req, issue_flags);
if (ret < 0)
@ -1088,16 +1086,15 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
rw->len = 0; /* similarly to above, reset len to 0 */
if (io_req_post_cqe(req, ret, cflags | IORING_CQE_F_MORE)) {
if (issue_flags & IO_URING_F_MULTISHOT) {
if (issue_flags & IO_URING_F_MULTISHOT)
/*
* Force retry, as we might have more data to
* be read and otherwise it won't get retried
* until (if ever) another poll is triggered.
*/
io_poll_multishot_retry(req);
return IOU_ISSUE_SKIP_COMPLETE;
}
return -EAGAIN;
return IOU_RETRY;
}
}