[PATCH for-next] io_uring: do not always force run task_work in io_uring_register

[PATCH for-next] io_uring: do not always force run task_work in io_uring_register

[Dylan Yudaken]

Running task work when not needed can unnecessarily delay
operations. Specifically IORING_SETUP_DEFER_TASKRUN tries to avoid running
task work until the user requests it. Therefore do not run it in
io_uring_register any more.

The one catch is that io_rsrc_ref_quiesce expects it to have run in order
to process all outstanding references, and so reorder it's loop to do this.

Signed-off-by: Dylan Yudaken <dylany@meta.com>
---

Note: I will send a separate liburing test case that would fail without the
changes to io_rsrc_ref_quiesce.


 io_uring/io_uring.c | 2 --
 io_uring/rsrc.c     | 7 ++++++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index db0dec120f09..112a5918e653 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -4050,8 +4050,6 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
 
 	ctx = f.file->private_data;
 
-	io_run_task_work_ctx(ctx);
-
 	mutex_lock(&ctx->uring_lock);
 	ret = __io_uring_register(ctx, opcode, arg, nr_args);
 	mutex_unlock(&ctx->uring_lock);
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 55d4ab96fb92..187f1c83e779 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -321,6 +321,11 @@ __cold static int io_rsrc_ref_quiesce(struct io_rsrc_data *data,
 		if (atomic_dec_and_test(&data->refs))
 			break;
 		mutex_unlock(&ctx->uring_lock);
+
+		ret = io_run_task_work_sig(ctx);
+		if (ret < 0)
+			goto reinit;
+
 		flush_delayed_work(&ctx->rsrc_put_work);
 		ret = wait_for_completion_interruptible(&data->done);
 		if (!ret) {
@@ -336,12 +341,12 @@ __cold static int io_rsrc_ref_quiesce(struct io_rsrc_data *data,
 			}
 		}
 
+reinit:
 		atomic_inc(&data->refs);
 		/* wait for all works potentially completing data->done */
 		flush_delayed_work(&ctx->rsrc_put_work);
 		reinit_completion(&data->done);
 
-		ret = io_run_task_work_sig(ctx);
 		mutex_lock(&ctx->uring_lock);
 	} while (ret >= 0);
 	data->quiesce = false;

base-commit: 765d0e263fccc8b22efef8258c3260e9d0ecf632
-- 
2.30.2

Re: [PATCH for-next] io_uring: do not always force run task_work in io_uring_register

[Jens Axboe]

On Mon, 7 Nov 2022 04:33:49 -0800, Dylan Yudaken wrote:
> Running task work when not needed can unnecessarily delay
> operations. Specifically IORING_SETUP_DEFER_TASKRUN tries to avoid running
> task work until the user requests it. Therefore do not run it in
> io_uring_register any more.
> 
> The one catch is that io_rsrc_ref_quiesce expects it to have run in order
> to process all outstanding references, and so reorder it's loop to do this.
> 
> [...]

Applied, thanks!

[1/1] io_uring: do not always force run task_work in io_uring_register
      commit: 462f399f87496aa71968ed863994f0db5b170ea3

Best regards,
-- 
Jens Axboe