在 2021/4/2 上午6:29, Pavel Begunkov 写道:
On 01/04/2021 15:55, Hao Xu wrote:
在 2021/4/1 下午6:25, Pavel Begunkov 写道:
On 01/04/2021 07:53, Hao Xu wrote:
在 2021/4/1 上午6:06, Pavel Begunkov 写道:
On 31/03/2021 10:01, Hao Xu wrote:
Now that we have multishot poll requests, one sqe can emit multiple
cqes. given below example:
sqe0(multishot poll)-->sqe1-->sqe2(drain req)
sqe2 is designed to issue after sqe0 and sqe1 completed, but since sqe0
is a multishot poll request, sqe2 may be issued after sqe0's event
triggered twice before sqe1 completed. This isn't what users leverage
drain requests for.
Here a simple solution is to ignore all multishot poll cqes, which means
drain requests won't wait those request to be done.
Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
---
fs/io_uring.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 513096759445..cd6d44cf5940 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -455,6 +455,7 @@ struct io_ring_ctx {
struct callback_head *exit_task_work;
struct wait_queue_head hash_wait;
+ unsigned multishot_cqes;
/* Keep this last, we don't need it for the fast path */
struct work_struct exit_work;
@@ -1181,8 +1182,8 @@ static bool req_need_defer(struct io_kiocb *req, u32 seq)
if (unlikely(req->flags & REQ_F_IO_DRAIN)) {
struct io_ring_ctx *ctx = req->ctx;
- return seq != ctx->cached_cq_tail
- + READ_ONCE(ctx->cached_cq_overflow);
+ return seq + ctx->multishot_cqes != ctx->cached_cq_tail
+ + READ_ONCE(ctx->cached_cq_overflow);
}
return false;
@@ -4897,6 +4898,7 @@ static bool io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
{
struct io_ring_ctx *ctx = req->ctx;
unsigned flags = IORING_CQE_F_MORE;
+ bool multishot_poll = !(req->poll.events & EPOLLONESHOT);
if (!error && req->poll.canceled) {
error = -ECANCELED;
@@ -4911,6 +4913,9 @@ static bool io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
req->poll.done = true;
flags = 0;
}
+ if (multishot_poll)
+ ctx->multishot_cqes++;
+
We need to make sure we do that only for a non-final complete, i.e.
not killing request, otherwise it'll double account the last one.
Hi Pavel, I saw a killing request like iopoll_remove or async_cancel call io_cqring_fill_event() to create an ECANCELED cqe for the original poll request. So there could be cases like(even for single poll request):
(1). add poll --> cancel poll, an ECANCELED cqe.
1sqe:1cqe all good
(2). add poll --> trigger event(queued to task_work) --> cancel poll, an ECANCELED cqe --> task_work runs, another ECANCELED cqe.
1sqe:2cqes
Those should emit a CQE on behalf of the request they're cancelling
only when it's definitely cancelled and not going to fill it
itself. E.g. if io_poll_cancel() found it and removed from
all the list and core's poll infra.
At least before multi-cqe it should have been working fine.
I haven't done a test for this, but from the code logic, there could be
case below:
io_poll_add() | io_poll_remove
(event happen)io_poll_wake() | io_poll_remove_one
| io_poll_remove_waitqs
| io_cqring_fill_event(-ECANCELED)
|
task_work run(io_poll_task_func) |
io_poll_complete() |
req->poll.canceled is true, \ |
__io_cqring_fill_event(-ECANCELED) |
two ECANCELED cqes, is there anything I missed?
Definitely may be be, but need to take a closer look
I'll do some test to test if this issue exists, and make some change if
it does.
I suggest we shall only emit one ECANCELED cqe.
Currently I only account cqe through io_poll_complete(), so ECANCELED cqe from io_poll_remove or async_cancel etc are not counted in.
E.g. is failed __io_cqring_fill_event() in io_poll_complete() fine?
Other places?
a failed __io_cqring_fill_event() doesn't produce a cqe but increment ctx->cached_cq_overflow, as long as a cqe is produced or cached_cq_overflow is +=1, it is ok.
Not claiming that the case is broken, but cached_cq_overflow is
considered in req_need_defer() as well, so from its perspective there
is no much difference between succeed fill_event() or not.
Btw, we can use some tests :)
I'll do more tests.
Perfect!
io_commit_cqring(ctx);
return !(flags & IORING_CQE_F_MORE);
}
