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* [RFC 1/1] io_uring: pin context while queueing deferred tw
@ 2023-01-04  1:34 Pavel Begunkov
  2023-01-04  1:36 ` Pavel Begunkov
  0 siblings, 1 reply; 3+ messages in thread
From: Pavel Begunkov @ 2023-01-04  1:34 UTC (permalink / raw)
  To: io-uring; +Cc: Jens Axboe, asml.silence

Unlike normal tw, nothing prevents deferred tw to be executed right
after an tw item added to ->work_llist in io_req_local_work_add(). For
instance, the waiting task may get waken up by CQ posting or a normal
tw. Thus we need to pin the ring for the rest of io_req_local_work_add()

Cc: [email protected]
Fixes: c0e0d6ba25f18 ("io_uring: add IORING_SETUP_DEFER_TASKRUN")
Signed-off-by: Pavel Begunkov <[email protected]>
---
 io_uring/io_uring.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 58ac13b69dc8..6bed44855679 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1236,13 +1236,18 @@ static void io_req_local_work_add(struct io_kiocb *req)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 
-	if (!llist_add(&req->io_task_work.node, &ctx->work_llist))
+	percpu_ref_get(&ctx->refs);
+
+	if (!llist_add(&req->io_task_work.node, &ctx->work_llist)) {
+		percpu_ref_put(&ctx->refs);
 		return;
+	}
 	/* need it for the following io_cqring_wake() */
 	smp_mb__after_atomic();
 
 	if (unlikely(atomic_read(&req->task->io_uring->in_idle))) {
 		io_move_task_work_from_local(ctx);
+		percpu_ref_put(&ctx->refs);
 		return;
 	}
 
@@ -1252,6 +1257,7 @@ static void io_req_local_work_add(struct io_kiocb *req)
 	if (ctx->has_evfd)
 		io_eventfd_signal(ctx);
 	__io_cqring_wake(ctx);
+	percpu_ref_put(&ctx->refs);
 }
 
 void __io_req_task_work_add(struct io_kiocb *req, bool allow_local)
-- 
2.38.1


^ permalink raw reply related	[flat|nested] 3+ messages in thread

* Re: [RFC 1/1] io_uring: pin context while queueing deferred tw
  2023-01-04  1:34 Pavel Begunkov
@ 2023-01-04  1:36 ` Pavel Begunkov
  0 siblings, 0 replies; 3+ messages in thread
From: Pavel Begunkov @ 2023-01-04  1:36 UTC (permalink / raw)
  To: io-uring; +Cc: Jens Axboe

On 1/4/23 01:34, Pavel Begunkov wrote:

Damn, the subj is wrong, it's not an RFC. Same with the other patch

> Unlike normal tw, nothing prevents deferred tw to be executed right
> after an tw item added to ->work_llist in io_req_local_work_add(). For
> instance, the waiting task may get waken up by CQ posting or a normal
> tw. Thus we need to pin the ring for the rest of io_req_local_work_add()
> 
> Cc: [email protected]
> Fixes: c0e0d6ba25f18 ("io_uring: add IORING_SETUP_DEFER_TASKRUN")

-- 
Pavel Begunkov

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [RFC 1/1] io_uring: pin context while queueing deferred tw
@ 2023-01-04 16:13 Jens Axboe
  0 siblings, 0 replies; 3+ messages in thread
From: Jens Axboe @ 2023-01-04 16:13 UTC (permalink / raw)
  To: io-uring, Pavel Begunkov


On Wed, 04 Jan 2023 01:34:02 +0000, Pavel Begunkov wrote:
> Unlike normal tw, nothing prevents deferred tw to be executed right
> after an tw item added to ->work_llist in io_req_local_work_add(). For
> instance, the waiting task may get waken up by CQ posting or a normal
> tw. Thus we need to pin the ring for the rest of io_req_local_work_add()
> 
> 

Applied, thanks!

[1/1] io_uring: pin context while queueing deferred tw
      (no commit info)

Best regards,
-- 
Jens Axboe



^ permalink raw reply	[flat|nested] 3+ messages in thread

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