[PATCHSET 0/2] io_uring async poll fixes

[PATCHSET 0/2] io_uring async poll fixes

[Jens Axboe]

Just two minor fixes here that should go into 5.7:

- Honor async request cancelation instead of trying to re-issue when
  it triggers

- Apply same re-wait approach for async poll that we do for regular poll,
  in case we get spurious wakeups.

-- 
Jens Axboe

[PATCH 1/2] io_uring: check for need to re-wait in polled async handling

[Jens Axboe]

We added this for just the regular poll requests in commit a6ba632d2c24
("io_uring: retry poll if we got woken with non-matching mask"), we
should do the same for the poll handler used pollable async requests.
Move the re-wait check and arm into a helper, and call it from
io_async_task_func() as well.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 43 +++++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0d1b5d5f1251..7b41f6231955 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4156,6 +4156,26 @@ static int __io_async_wake(struct io_kiocb *req, struct io_poll_iocb *poll,
 	return 1;
 }
 
+static bool io_poll_rewait(struct io_kiocb *req, struct io_poll_iocb *poll)
+	__acquires(&req->ctx->completion_lock)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	if (!req->result && !READ_ONCE(poll->canceled)) {
+		struct poll_table_struct pt = { ._key = poll->events };
+
+		req->result = vfs_poll(req->file, &pt) & poll->events;
+	}
+
+	spin_lock_irq(&ctx->completion_lock);
+	if (!req->result && !READ_ONCE(poll->canceled)) {
+		add_wait_queue(poll->head, &poll->wait);
+		return true;
+	}
+
+	return false;
+}
+
 static void io_async_task_func(struct callback_head *cb)
 {
 	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
@@ -4164,14 +4184,16 @@ static void io_async_task_func(struct callback_head *cb)
 
 	trace_io_uring_task_run(req->ctx, req->opcode, req->user_data);
 
-	WARN_ON_ONCE(!list_empty(&req->apoll->poll.wait.entry));
-
-	if (hash_hashed(&req->hash_node)) {
-		spin_lock_irq(&ctx->completion_lock);
-		hash_del(&req->hash_node);
+	if (io_poll_rewait(req, &apoll->poll)) {
 		spin_unlock_irq(&ctx->completion_lock);
+		return;
 	}
 
+	if (hash_hashed(&req->hash_node))
+		hash_del(&req->hash_node);
+
+	spin_unlock_irq(&ctx->completion_lock);
+
 	/* restore ->work in case we need to retry again */
 	memcpy(&req->work, &apoll->work, sizeof(req->work));
 
@@ -4436,18 +4458,11 @@ static void io_poll_task_handler(struct io_kiocb *req, struct io_kiocb **nxt)
 	struct io_ring_ctx *ctx = req->ctx;
 	struct io_poll_iocb *poll = &req->poll;
 
-	if (!req->result && !READ_ONCE(poll->canceled)) {
-		struct poll_table_struct pt = { ._key = poll->events };
-
-		req->result = vfs_poll(req->file, &pt) & poll->events;
-	}
-
-	spin_lock_irq(&ctx->completion_lock);
-	if (!req->result && !READ_ONCE(poll->canceled)) {
-		add_wait_queue(poll->head, &poll->wait);
+	if (io_poll_rewait(req, poll)) {
 		spin_unlock_irq(&ctx->completion_lock);
 		return;
 	}
+
 	hash_del(&req->hash_node);
 	io_poll_complete(req, req->result, 0);
 	req->flags |= REQ_F_COMP_LOCKED;
-- 
2.26.0

[PATCH 2/2] io_uring: io_async_task_func() should check and honor cancelation

[Jens Axboe]

If the request has been marked as canceled, don't try and issue it.
Instead just fill a canceled event and finish the request.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7b41f6231955..2f9e93892870 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4181,6 +4181,7 @@ static void io_async_task_func(struct callback_head *cb)
 	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
 	struct async_poll *apoll = req->apoll;
 	struct io_ring_ctx *ctx = req->ctx;
+	bool canceled;
 
 	trace_io_uring_task_run(req->ctx, req->opcode, req->user_data);
 
@@ -4192,8 +4193,21 @@ static void io_async_task_func(struct callback_head *cb)
 	if (hash_hashed(&req->hash_node))
 		hash_del(&req->hash_node);
 
+	canceled = READ_ONCE(apoll->poll.canceled);
+	if (canceled) {
+		io_cqring_fill_event(req, -ECANCELED);
+		io_commit_cqring(ctx);
+	}
+
 	spin_unlock_irq(&ctx->completion_lock);
 
+	if (canceled) {
+		kfree(apoll);
+		io_cqring_ev_posted(ctx);
+		req_set_fail_links(req);
+		io_put_req(req);
+	}
+
 	/* restore ->work in case we need to retry again */
 	memcpy(&req->work, &apoll->work, sizeof(req->work));
 
-- 
2.26.0

Re: [PATCHSET 0/2] io_uring async poll fixes

[Jens Axboe]

On 4/13/20 11:21 AM, Jens Axboe wrote:
> Just two minor fixes here that should go into 5.7:
> 
> - Honor async request cancelation instead of trying to re-issue when
>   it triggers
> 
> - Apply same re-wait approach for async poll that we do for regular poll,
>   in case we get spurious wakeups.

Please see v2 instead:

https://lore.kernel.org/io-uring/20200413172606.8836-1-axboe@kernel.dk/T/#u

-- 
Jens Axboe