io_uring: consolidate overflow flushing

Consolidate __io_cqring_overflow_flush and io_cqring_overflow_kill()
into a single function as it once was, it's easier to work with it this
way.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/986b42c35e76a6be7aa0cdcda0a236a2222da3a7.1712708261.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/io_uring.c

@@ -668,26 +668,7 @@ static void io_cq_unlock_post(struct io_ring_ctx *ctx)
 	io_commit_cqring_flush(ctx);
 }
 
-static void io_cqring_overflow_kill(struct io_ring_ctx *ctx)
-{
-	struct io_overflow_cqe *ocqe;
-	LIST_HEAD(list);
-
-	lockdep_assert_held(&ctx->uring_lock);
-
-	spin_lock(&ctx->completion_lock);
-	list_splice_init(&ctx->cq_overflow_list, &list);
-	clear_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq);
-	spin_unlock(&ctx->completion_lock);
-
-	while (!list_empty(&list)) {
-		ocqe = list_first_entry(&list, struct io_overflow_cqe, list);
-		list_del(&ocqe->list);
-		kfree(ocqe);
-	}
-}
-
-static void __io_cqring_overflow_flush(struct io_ring_ctx *ctx)
+static void __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool dying)
 {
 	size_t cqe_size = sizeof(struct io_uring_cqe);
 
@@ -704,11 +685,14 @@ static void __io_cqring_overflow_flush(struct io_ring_ctx *ctx)
 		struct io_uring_cqe *cqe;
 		struct io_overflow_cqe *ocqe;
 
-		if (!io_get_cqe_overflow(ctx, &cqe, true))
-			break;
 		ocqe = list_first_entry(&ctx->cq_overflow_list,
 					struct io_overflow_cqe, list);
-		memcpy(cqe, &ocqe->cqe, cqe_size);
+
+		if (!dying) {
+			if (!io_get_cqe_overflow(ctx, &cqe, true))
+				break;
+			memcpy(cqe, &ocqe->cqe, cqe_size);
+		}
 		list_del(&ocqe->list);
 		kfree(ocqe);
 	}
@@ -720,10 +704,16 @@ static void __io_cqring_overflow_flush(struct io_ring_ctx *ctx)
 	io_cq_unlock_post(ctx);
 }
 
+static void io_cqring_overflow_kill(struct io_ring_ctx *ctx)
+{
+	if (ctx->rings)
+		__io_cqring_overflow_flush(ctx, true);
+}
+
 static void io_cqring_do_overflow_flush(struct io_ring_ctx *ctx)
 {
 	mutex_lock(&ctx->uring_lock);
-	__io_cqring_overflow_flush(ctx);
+	__io_cqring_overflow_flush(ctx, false);
 	mutex_unlock(&ctx->uring_lock);
 }
 
@@ -1531,7 +1521,7 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
 	check_cq = READ_ONCE(ctx->check_cq);
 	if (unlikely(check_cq)) {
 		if (check_cq & BIT(IO_CHECK_CQ_OVERFLOW_BIT))
-			__io_cqring_overflow_flush(ctx);
+			__io_cqring_overflow_flush(ctx, false);
 		/*
 		 * Similarly do not spin if we have not informed the user of any
 		 * dropped CQE.