[PATCH v2] io_uring: add support for multishot timeouts

[David Wei <davidhwei@meta.com>]

A multishot timeout submission will repeatedly generate completions with
the IORING_CQE_F_MORE cflag set. Depending on the value of the `off' field
in the submission, these timeouts can either repeat indefinitely until
cancelled (`off' = 0) or for a fixed number of times (`off' > 0).

Only noseq timeouts (i.e. not dependent on the number of I/O
completions) are supported.

An indefinite timer will be cancelled with EOVERFLOW if the CQ ever
overflows.

Signed-off-by: David Wei <davidhwei@meta.com>
---
 include/uapi/linux/io_uring.h |  1 +
 io_uring/timeout.c            | 59 +++++++++++++++++++++++++++++++++--
 2 files changed, 57 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index f8d14d1c58d3..0716cb17e436 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -250,6 +250,7 @@ enum io_uring_op {
 #define IORING_TIMEOUT_REALTIME		(1U << 3)
 #define IORING_LINK_TIMEOUT_UPDATE	(1U << 4)
 #define IORING_TIMEOUT_ETIME_SUCCESS	(1U << 5)
+#define IORING_TIMEOUT_MULTISHOT	(1U << 6)
 #define IORING_TIMEOUT_CLOCK_MASK	(IORING_TIMEOUT_BOOTTIME | IORING_TIMEOUT_REALTIME)
 #define IORING_TIMEOUT_UPDATE_MASK	(IORING_TIMEOUT_UPDATE | IORING_LINK_TIMEOUT_UPDATE)
 /*
diff --git a/io_uring/timeout.c b/io_uring/timeout.c
index 5c6c6f720809..61b8488565ce 100644
--- a/io_uring/timeout.c
+++ b/io_uring/timeout.c
@@ -17,6 +17,7 @@ struct io_timeout {
 	struct file			*file;
 	u32				off;
 	u32				target_seq;
+	u32				repeats;
 	struct list_head		list;
 	/* head of the link, used by linked timeouts only */
 	struct io_kiocb			*head;
@@ -37,8 +38,9 @@ struct io_timeout_rem {
 static inline bool io_is_timeout_noseq(struct io_kiocb *req)
 {
 	struct io_timeout *timeout = io_kiocb_to_cmd(req, struct io_timeout);
+	struct io_timeout_data *data = req->async_data;
 
-	return !timeout->off;
+	return !timeout->off || data->flags & IORING_TIMEOUT_MULTISHOT;
 }
 
 static inline void io_put_req(struct io_kiocb *req)
@@ -49,6 +51,45 @@ static inline void io_put_req(struct io_kiocb *req)
 	}
 }
 
+static inline bool io_timeout_finish(struct io_timeout *timeout,
+				     struct io_timeout_data *data)
+{
+	if (!(data->flags & IORING_TIMEOUT_MULTISHOT))
+		return true;
+
+	if (!timeout->off || (timeout->repeats && --timeout->repeats))
+		return false;
+
+	return true;
+}
+
+static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer);
+
+static void io_timeout_complete(struct io_kiocb *req, struct io_tw_state *ts)
+{
+	struct io_timeout *timeout = io_kiocb_to_cmd(req, struct io_timeout);
+	struct io_timeout_data *data = req->async_data;
+	struct io_ring_ctx *ctx = req->ctx;
+
+	if (!io_timeout_finish(timeout, data)) {
+		bool filled;
+		filled = io_aux_cqe(ctx, false, req->cqe.user_data, -ETIME,
+				      IORING_CQE_F_MORE, false);
+		if (filled) {
+			/* re-arm timer */
+			spin_lock_irq(&ctx->timeout_lock);
+			list_add(&timeout->list, ctx->timeout_list.prev);
+			data->timer.function = io_timeout_fn;
+			hrtimer_start(&data->timer, timespec64_to_ktime(data->ts), data->mode);
+			spin_unlock_irq(&ctx->timeout_lock);
+			return;
+		}
+		io_req_set_res(req, -EOVERFLOW, 0);
+	}
+
+	io_req_task_complete(req, ts);
+}
+
 static bool io_kill_timeout(struct io_kiocb *req, int status)
 	__must_hold(&req->ctx->timeout_lock)
 {
@@ -212,7 +253,7 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer)
 		req_set_fail(req);
 
 	io_req_set_res(req, -ETIME, 0);
-	req->io_task_work.func = io_req_task_complete;
+	req->io_task_work.func = io_timeout_complete;
 	io_req_task_work_add(req);
 	return HRTIMER_NORESTART;
 }
@@ -470,16 +511,28 @@ static int __io_timeout_prep(struct io_kiocb *req,
 		return -EINVAL;
 	flags = READ_ONCE(sqe->timeout_flags);
 	if (flags & ~(IORING_TIMEOUT_ABS | IORING_TIMEOUT_CLOCK_MASK |
-		      IORING_TIMEOUT_ETIME_SUCCESS))
+		      IORING_TIMEOUT_ETIME_SUCCESS |
+		      IORING_TIMEOUT_MULTISHOT)) {
 		return -EINVAL;
+	}
 	/* more than one clock specified is invalid, obviously */
 	if (hweight32(flags & IORING_TIMEOUT_CLOCK_MASK) > 1)
 		return -EINVAL;
+	/* multishot requests only make sense with rel values */
+	if (!(~flags & (IORING_TIMEOUT_MULTISHOT | IORING_TIMEOUT_ABS)))
+		return -EINVAL;
 
 	INIT_LIST_HEAD(&timeout->list);
 	timeout->off = off;
 	if (unlikely(off && !req->ctx->off_timeout_used))
 		req->ctx->off_timeout_used = true;
+	/*
+	 * for multishot reqs w/ fixed nr of repeats, target_seq tracks the
+	 * remaining nr
+	 */
+	timeout->repeats = 0;
+	if ((flags & IORING_TIMEOUT_MULTISHOT) && off > 0)
+		timeout->repeats = off;
 
 	if (WARN_ON_ONCE(req_has_async_data(req)))
 		return -EFAULT;
-- 
2.34.1