[PATCH 5.12] io_uring: clean R_DISABLED startup mess

[PATCH 5.12] io_uring: clean R_DISABLED startup mess

[Pavel Begunkov]

There are enough of problems with IORING_SETUP_R_DISABLED, including the
burden of checking and kicking off the SQO task all over the codebase --
for exit/cancel/etc.

Rework it, always start the thread but don't do submit unless the flag
is gone, that's much easier.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 25 ++++++-------------------
 1 file changed, 6 insertions(+), 19 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5c6a54520be0..5ef9f836cccc 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6607,7 +6607,8 @@ static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
 		if (!list_empty(&ctx->iopoll_list))
 			io_do_iopoll(ctx, &nr_events, 0);
 
-		if (to_submit && likely(!percpu_ref_is_dying(&ctx->refs)))
+		if (to_submit && likely(!percpu_ref_is_dying(&ctx->refs)) &&
+		    !(ctx->flags & IORING_SETUP_R_DISABLED))
 			ret = io_submit_sqes(ctx, to_submit);
 		mutex_unlock(&ctx->uring_lock);
 	}
@@ -7865,6 +7866,7 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
 		wake_up_new_task(tsk);
 		if (ret)
 			goto err;
+		complete(&sqd->startup);
 	} else if (p->flags & IORING_SETUP_SQ_AFF) {
 		/* Can't have SQ_AFF without SQPOLL */
 		ret = -EINVAL;
@@ -7877,15 +7879,6 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
 	return ret;
 }
 
-static void io_sq_offload_start(struct io_ring_ctx *ctx)
-{
-	struct io_sq_data *sqd = ctx->sq_data;
-
-	ctx->flags &= ~IORING_SETUP_R_DISABLED;
-	if (ctx->flags & IORING_SETUP_SQPOLL)
-		complete(&sqd->startup);
-}
-
 static inline void __io_unaccount_mem(struct user_struct *user,
 				      unsigned long nr_pages)
 {
@@ -8746,11 +8739,6 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
 	struct task_struct *task = current;
 
 	if ((ctx->flags & IORING_SETUP_SQPOLL) && ctx->sq_data) {
-		/* never started, nothing to cancel */
-		if (ctx->flags & IORING_SETUP_R_DISABLED) {
-			io_sq_offload_start(ctx);
-			return;
-		}
 		io_sq_thread_park(ctx->sq_data);
 		task = ctx->sq_data->thread;
 		if (task)
@@ -9453,9 +9441,6 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
 	if (ret)
 		goto err;
 
-	if (!(p->flags & IORING_SETUP_R_DISABLED))
-		io_sq_offload_start(ctx);
-
 	memset(&p->sq_off, 0, sizeof(p->sq_off));
 	p->sq_off.head = offsetof(struct io_rings, sq.head);
 	p->sq_off.tail = offsetof(struct io_rings, sq.tail);
@@ -9672,7 +9657,9 @@ static int io_register_enable_rings(struct io_ring_ctx *ctx)
 	if (ctx->restrictions.registered)
 		ctx->restricted = 1;
 
-	io_sq_offload_start(ctx);
+	ctx->flags &= ~IORING_SETUP_R_DISABLED;
+	if (ctx->sq_data && wq_has_sleeper(&ctx->sq_data->wait))
+		wake_up(&ctx->sq_data->wait);
 	return 0;
 }
 
-- 
2.24.0

Re: [PATCH 5.12] io_uring: clean R_DISABLED startup mess

[Jens Axboe]

On 3/8/21 6:20 AM, Pavel Begunkov wrote:
> There are enough of problems with IORING_SETUP_R_DISABLED, including the
> burden of checking and kicking off the SQO task all over the codebase --
> for exit/cancel/etc.
> 
> Rework it, always start the thread but don't do submit unless the flag
> is gone, that's much easier.

This is a good simplification, much better than having the weird
state that is not started.

-- 
Jens Axboe