On 9/8/23 14:49, Jens Axboe wrote:
On 9/8/23 3:30 AM, Ming Lei wrote:
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index ad636954abae..95a3d31a1ef1 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1930,6 +1930,10 @@ void io_wq_submit_work(struct io_wq_work *work)
}
}
+ /* It is fragile to block POLLED IO, so switch to NON_BLOCK */
+ if ((req->ctx->flags & IORING_SETUP_IOPOLL) && def->iopoll_queue)
+ issue_flags |= IO_URING_F_NONBLOCK;
+
I think this comment deserves to be more descriptive. Normally we
absolutely cannot block for polled IO, it's only OK here because io-wq
is the issuer and not necessarily the poller of it. That generally falls
upon the original issuer to poll these requests.
I think this should be a separate commit, coming before the main fix
which is below.
@@ -3363,6 +3367,12 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
finish_wait(&tctx->wait, &wait);
} while (1);
+ /*
+ * Reap events from each ctx, otherwise these requests may take
+ * resources and prevent other contexts from being moved on.
+ */
+ xa_for_each(&tctx->xa, index, node)
+ io_iopoll_try_reap_events(node->ctx);
The main issue here is that if someone isn't polling for them, then we
get to wait for a timeout before they complete. This can delay exit, for
example, as we're now just waiting 30 seconds (or whatever the timeout
is on the underlying device) for them to get timed out before exit can
finish.
Ok, our case is that userspace crashes and doesn't poll for its IO.
How would that block io-wq termination? We send a signal and workers
should exit, either by queueing up the request for iopoll (and then
we queue it into the io_uring iopoll list and the worker immediately
returns back and presumably exits), or it fails because of the signal
and returns back.
That should kill all io-wq and make exit go forward. Then the io_uring
file will be destroyed and the ring exit work will be polling via
io_ring_exit_work();
-- io_uring_try_cancel_requests();
-- io_iopoll_try_reap_events();
What I'm missing? Does the blocking change make io-wq iopolling
completions inside the block? Was it by any chance with the recent
"do_exit() waiting for ring destruction" patches?
--
Pavel Begunkov
