[RFC][PATCH] io_uring: Incapsulate conditional mem accounting

["Pavel Begunkov (Silence)" <asml.silence@xxxxxxxxx>]

From: Pavel Begunkov <asml.silence@xxxxxxxxx>

It's quite tedious and error-prone to manually check before each call
to io_{,un}account_mem() whether we need memory accounting. Instead,
the functions can work directly with struct io_ring_ctx and handle
checks themselves. In any case, they're perfectly inlined.

Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 fs/io_uring.c | 59 ++++++++++++++++++++++-----------------------------
 1 file changed, 25 insertions(+), 34 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 3fd884b4e0be..f47f7abe19eb 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2704,14 +2704,19 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
 	return ret;
 }
 
-static void io_unaccount_mem(struct user_struct *user, unsigned long nr_pages)
+static void io_unaccount_mem(struct io_ring_ctx *ctx, unsigned long nr_pages)
 {
-	atomic_long_sub(nr_pages, &user->locked_vm);
+	if (ctx->account_mem)
+		atomic_long_sub(nr_pages, &ctx->user->locked_vm);
 }
 
-static int io_account_mem(struct user_struct *user, unsigned long nr_pages)
+static int io_account_mem(struct io_ring_ctx *ctx, unsigned long nr_pages)
 {
 	unsigned long page_limit, cur_pages, new_pages;
+	struct user_struct *user = ctx->user;
+
+	if (!ctx->account_mem)
+		return 0;
 
 	/* Don't allow more pages than we can safely lock */
 	page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
@@ -2773,8 +2778,7 @@ static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
 		for (j = 0; j < imu->nr_bvecs; j++)
 			put_page(imu->bvec[j].bv_page);
 
-		if (ctx->account_mem)
-			io_unaccount_mem(ctx->user, imu->nr_bvecs);
+		io_unaccount_mem(ctx, imu->nr_bvecs);
 		kvfree(imu->bvec);
 		imu->nr_bvecs = 0;
 	}
@@ -2857,11 +2861,9 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 		start = ubuf >> PAGE_SHIFT;
 		nr_pages = end - start;
 
-		if (ctx->account_mem) {
-			ret = io_account_mem(ctx->user, nr_pages);
-			if (ret)
-				goto err;
-		}
+		ret = io_account_mem(ctx, nr_pages);
+		if (ret)
+			goto err;
 
 		ret = 0;
 		if (!pages || nr_pages > got_pages) {
@@ -2874,8 +2876,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 					GFP_KERNEL);
 			if (!pages || !vmas) {
 				ret = -ENOMEM;
-				if (ctx->account_mem)
-					io_unaccount_mem(ctx->user, nr_pages);
+				io_unaccount_mem(ctx, nr_pages);
 				goto err;
 			}
 			got_pages = nr_pages;
@@ -2885,8 +2886,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 						GFP_KERNEL);
 		ret = -ENOMEM;
 		if (!imu->bvec) {
-			if (ctx->account_mem)
-				io_unaccount_mem(ctx->user, nr_pages);
+			io_unaccount_mem(ctx, nr_pages);
 			goto err;
 		}
 
@@ -2919,8 +2919,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 				for (j = 0; j < pret; j++)
 					put_page(pages[j]);
 			}
-			if (ctx->account_mem)
-				io_unaccount_mem(ctx->user, nr_pages);
+			io_unaccount_mem(ctx, nr_pages);
 			kvfree(imu->bvec);
 			goto err;
 		}
@@ -3009,9 +3008,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_mem_free(ctx->cq_ring);
 
 	percpu_ref_exit(&ctx->refs);
-	if (ctx->account_mem)
-		io_unaccount_mem(ctx->user,
-				ring_pages(ctx->sq_entries, ctx->cq_entries));
+	io_unaccount_mem(ctx, ring_pages(ctx->sq_entries, ctx->cq_entries));
 	free_uid(ctx->user);
 	kfree(ctx);
 }
@@ -3253,7 +3250,6 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
 {
 	struct user_struct *user = NULL;
 	struct io_ring_ctx *ctx;
-	bool account_mem;
 	int ret;
 
 	if (!entries || entries > IORING_MAX_ENTRIES)
@@ -3269,29 +3265,24 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
 	p->cq_entries = 2 * p->sq_entries;
 
 	user = get_uid(current_user());
-	account_mem = !capable(CAP_IPC_LOCK);
-
-	if (account_mem) {
-		ret = io_account_mem(user,
-				ring_pages(p->sq_entries, p->cq_entries));
-		if (ret) {
-			free_uid(user);
-			return ret;
-		}
-	}
 
 	ctx = io_ring_ctx_alloc(p);
 	if (!ctx) {
-		if (account_mem)
-			io_unaccount_mem(user, ring_pages(p->sq_entries,
-								p->cq_entries));
 		free_uid(user);
 		return -ENOMEM;
 	}
+
 	ctx->compat = in_compat_syscall();
-	ctx->account_mem = account_mem;
+	ctx->account_mem = !capable(CAP_IPC_LOCK);
 	ctx->user = user;
 
+	ret = io_account_mem(ctx, ring_pages(p->sq_entries, p->cq_entries));
+	if (ret) {
+		free_uid(user);
+		kfree(ctx);
+		return ret;
+	}
+
 	ret = io_allocate_scq_urings(ctx, p);
 	if (ret)
 		goto err;
-- 
2.22.0