[PATCH 1/2] io_uring: split alloc and add of overflow

[Jens Axboe <axboe@kernel.dk>]

Add a new helper, io_alloc_ocqe(), that simply allocates and fills an
overflow entry. Then it can get done outside of the locking section,
and hence use more appropriate gfp_t allocation flags rather than always
default to GFP_ATOMIC.

Suggested-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io_uring.c | 75 +++++++++++++++++++++++++++++----------------
 1 file changed, 48 insertions(+), 27 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 9a9b8d35349b..2519fab303c4 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -718,20 +718,11 @@ static __cold void io_uring_drop_tctx_refs(struct task_struct *task)
 	}
 }
 
-static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data,
-				     s32 res, u32 cflags, u64 extra1, u64 extra2)
+static bool io_cqring_add_overflow(struct io_ring_ctx *ctx,
+				   struct io_overflow_cqe *ocqe)
 {
-	struct io_overflow_cqe *ocqe;
-	size_t ocq_size = sizeof(struct io_overflow_cqe);
-	bool is_cqe32 = (ctx->flags & IORING_SETUP_CQE32);
-
 	lockdep_assert_held(&ctx->completion_lock);
 
-	if (is_cqe32)
-		ocq_size += sizeof(struct io_uring_cqe);
-
-	ocqe = kmalloc(ocq_size, GFP_ATOMIC | __GFP_ACCOUNT);
-	trace_io_uring_cqe_overflow(ctx, user_data, res, cflags, ocqe);
 	if (!ocqe) {
 		struct io_rings *r = ctx->rings;
 
@@ -749,22 +740,44 @@ static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data,
 		atomic_or(IORING_SQ_CQ_OVERFLOW, &ctx->rings->sq_flags);
 
 	}
-	ocqe->cqe.user_data = user_data;
-	ocqe->cqe.res = res;
-	ocqe->cqe.flags = cflags;
-	if (is_cqe32) {
-		ocqe->cqe.big_cqe[0] = extra1;
-		ocqe->cqe.big_cqe[1] = extra2;
-	}
 	list_add_tail(&ocqe->list, &ctx->cq_overflow_list);
 	return true;
 }
 
-static void io_req_cqe_overflow(struct io_kiocb *req)
+static struct io_overflow_cqe *io_alloc_ocqe(struct io_ring_ctx *ctx,
+					     u64 user_data, s32 res, u32 cflags,
+					     u64 extra1, u64 extra2, gfp_t gfp)
+{
+	struct io_overflow_cqe *ocqe;
+	size_t ocq_size = sizeof(struct io_overflow_cqe);
+	bool is_cqe32 = (ctx->flags & IORING_SETUP_CQE32);
+
+	if (is_cqe32)
+		ocq_size += sizeof(struct io_uring_cqe);
+
+	ocqe = kmalloc(ocq_size, gfp | __GFP_ACCOUNT);
+	trace_io_uring_cqe_overflow(ctx, user_data, res, cflags, ocqe);
+	if (ocqe) {
+		ocqe->cqe.user_data = user_data;
+		ocqe->cqe.res = res;
+		ocqe->cqe.flags = cflags;
+		if (is_cqe32) {
+			ocqe->cqe.big_cqe[0] = extra1;
+			ocqe->cqe.big_cqe[1] = extra2;
+		}
+	}
+	return ocqe;
+}
+
+static void io_req_cqe_overflow(struct io_kiocb *req, gfp_t gfp)
 {
-	io_cqring_event_overflow(req->ctx, req->cqe.user_data,
-				req->cqe.res, req->cqe.flags,
-				req->big_cqe.extra1, req->big_cqe.extra2);
+	struct io_ring_ctx *ctx = req->ctx;
+	struct io_overflow_cqe *ocqe;
+
+	ocqe = io_alloc_ocqe(ctx, req->cqe.user_data, req->cqe.res,
+			     req->cqe.flags, req->big_cqe.extra1,
+			     req->big_cqe.extra2, gfp);
+	io_cqring_add_overflow(ctx, ocqe);
 	memset(&req->big_cqe, 0, sizeof(req->big_cqe));
 }
 
@@ -832,8 +845,12 @@ bool io_post_aux_cqe(struct io_ring_ctx *ctx, u64 user_data, s32 res, u32 cflags
 
 	io_cq_lock(ctx);
 	filled = io_fill_cqe_aux(ctx, user_data, res, cflags);
-	if (!filled)
-		filled = io_cqring_event_overflow(ctx, user_data, res, cflags, 0, 0);
+	if (unlikely(!filled)) {
+		struct io_overflow_cqe *ocqe;
+
+		ocqe = io_alloc_ocqe(ctx, user_data, res, cflags, 0, 0, GFP_ATOMIC);
+		filled = io_cqring_add_overflow(ctx, ocqe);
+	}
 	io_cq_unlock_post(ctx);
 	return filled;
 }
@@ -848,8 +865,11 @@ void io_add_aux_cqe(struct io_ring_ctx *ctx, u64 user_data, s32 res, u32 cflags)
 	lockdep_assert(ctx->lockless_cq);
 
 	if (!io_fill_cqe_aux(ctx, user_data, res, cflags)) {
+		struct io_overflow_cqe *ocqe;
+
+		ocqe = io_alloc_ocqe(ctx, user_data, res, cflags, 0, 0, GFP_KERNEL);
 		spin_lock(&ctx->completion_lock);
-		io_cqring_event_overflow(ctx, user_data, res, cflags, 0, 0);
+		io_cqring_add_overflow(ctx, ocqe);
 		spin_unlock(&ctx->completion_lock);
 	}
 	ctx->submit_state.cq_flush = true;
@@ -1442,10 +1462,11 @@ void __io_submit_flush_completions(struct io_ring_ctx *ctx)
 		    unlikely(!io_fill_cqe_req(ctx, req))) {
 			if (ctx->lockless_cq) {
 				spin_lock(&ctx->completion_lock);
-				io_req_cqe_overflow(req);
+				io_req_cqe_overflow(req, GFP_ATOMIC);
 				spin_unlock(&ctx->completion_lock);
 			} else {
-				io_req_cqe_overflow(req);
+				gfp_t gfp = ctx->lockless_cq ? GFP_KERNEL : GFP_ATOMIC;
+				io_req_cqe_overflow(req, gfp);
 			}
 		}
 	}
-- 
2.49.0