[PATCH] io_uring: clear IORING_SQ_NEED_WAKEUP after executing task works

[PATCH] io_uring: clear IORING_SQ_NEED_WAKEUP after executing task works

[Xiaoguang Wang]

In io_sq_thread(), if there are task works to handle, current codes
will skip schedule() and go on polling sq again, but forget to clear
IORING_SQ_NEED_WAKEUP flag, fix this issue. Also add two helpers to
set and clear IORING_SQ_NEED_WAKEUP flag,

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
---
 fs/io_uring.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index cda729de4ea3..a4a0a5feabfd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6334,6 +6334,21 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
 	return submitted;
 }
 
+static inline void io_ring_set_wakeup_flag(struct io_ring_ctx *ctx)
+{
+	/* Tell userspace we may need a wakeup call */
+	spin_lock_irq(&ctx->completion_lock);
+	ctx->rings->sq_flags |= IORING_SQ_NEED_WAKEUP;
+	spin_unlock_irq(&ctx->completion_lock);
+}
+
+static inline void io_ring_clear_wakeup_flag(struct io_ring_ctx *ctx)
+{
+	spin_lock_irq(&ctx->completion_lock);
+	ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
+	spin_unlock_irq(&ctx->completion_lock);
+}
+
 static int io_sq_thread(void *data)
 {
 	struct io_ring_ctx *ctx = data;
@@ -6407,10 +6422,7 @@ static int io_sq_thread(void *data)
 				continue;
 			}
 
-			/* Tell userspace we may need a wakeup call */
-			spin_lock_irq(&ctx->completion_lock);
-			ctx->rings->sq_flags |= IORING_SQ_NEED_WAKEUP;
-			spin_unlock_irq(&ctx->completion_lock);
+			io_ring_set_wakeup_flag(ctx);
 
 			to_submit = io_sqring_entries(ctx);
 			if (!to_submit || ret == -EBUSY) {
@@ -6420,6 +6432,7 @@ static int io_sq_thread(void *data)
 				}
 				if (io_run_task_work()) {
 					finish_wait(&ctx->sqo_wait, &wait);
+					io_ring_clear_wakeup_flag(ctx);
 					continue;
 				}
 				if (signal_pending(current))
@@ -6427,17 +6440,13 @@ static int io_sq_thread(void *data)
 				schedule();
 				finish_wait(&ctx->sqo_wait, &wait);
 
-				spin_lock_irq(&ctx->completion_lock);
-				ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
-				spin_unlock_irq(&ctx->completion_lock);
+				io_ring_clear_wakeup_flag(ctx);
 				ret = 0;
 				continue;
 			}
 			finish_wait(&ctx->sqo_wait, &wait);
 
-			spin_lock_irq(&ctx->completion_lock);
-			ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
-			spin_unlock_irq(&ctx->completion_lock);
+			io_ring_clear_wakeup_flag(ctx);
 		}
 
 		mutex_lock(&ctx->uring_lock);
-- 
2.17.2

Re: [PATCH] io_uring: clear IORING_SQ_NEED_WAKEUP after executing task works

[Jens Axboe]

On 7/23/20 6:57 AM, Xiaoguang Wang wrote:
> In io_sq_thread(), if there are task works to handle, current codes
> will skip schedule() and go on polling sq again, but forget to clear
> IORING_SQ_NEED_WAKEUP flag, fix this issue. Also add two helpers to
> set and clear IORING_SQ_NEED_WAKEUP flag,

Was pondering if we should make the new helpers conditional ala:

static inline void io_ring_set_wakeup_flag(struct io_ring_ctx *ctx)
{
	/* Tell userspace we may need a wakeup call */
	if (!(ctx->rings->sq_flags & IORING_SQ_NEED_WAKEUP)) {
		spin_lock_irq(&ctx->completion_lock);
		ctx->rings->sq_flags |= IORING_SQ_NEED_WAKEUP;
		spin_unlock_irq(&ctx->completion_lock);
	}
}

static inline void io_ring_clear_wakeup_flag(struct io_ring_ctx *ctx)
{
	if (ctx->rings->sq_flags & IORING_SQ_NEED_WAKEUP) {
		spin_lock_irq(&ctx->completion_lock);
		ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
		spin_unlock_irq(&ctx->completion_lock);
	}
}

but don't see any need after looking closer. So patch looks fine to me,
thanks.

-- 
Jens Axboe