io_uring/rsrc: refactor io_rsrc_node_switch

We use io_rsrc_node_switch() coupled with io_rsrc_node_switch_start()
for a bunch of cases including initialising ctx->rsrc_node, i.e. by
passing NULL instead of rsrc_data. Leave it to only deal with actual
node changing.

For that, first remove it from io_uring_create() and add a function
allocating the first node. Then also remove all calls to
io_rsrc_node_switch() from files/buffers register as we already have a
node installed and it does essentially nothing.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d146fe306ff98b1a5a60c997c252534f03d423d7.1681210788.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/io_uring.c

@@ -3881,11 +3881,10 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
 	ret = io_sq_offload_create(ctx, p);
 	if (ret)
 		goto err;
-	/* always set a rsrc node */
-	ret = io_rsrc_node_switch_start(ctx);
+
+	ret = io_rsrc_init(ctx);
 	if (ret)
 		goto err;
-	io_rsrc_node_switch(ctx, NULL);
 
 	memset(&p->sq_off, 0, sizeof(p->sq_off));
 	p->sq_off.head = offsetof(struct io_rings, sq.head);

io_uring/rsrc.c

@@ -204,7 +204,7 @@ void io_rsrc_node_ref_zero(struct io_rsrc_node *node)
 	}
 }
 
-static struct io_rsrc_node *io_rsrc_node_alloc(struct io_ring_ctx *ctx)
+struct io_rsrc_node *io_rsrc_node_alloc(struct io_ring_ctx *ctx)
 {
 	struct io_rsrc_node *ref_node;
 	struct io_cache_entry *entry;
@@ -231,23 +231,18 @@ void io_rsrc_node_switch(struct io_ring_ctx *ctx,
 			 struct io_rsrc_data *data_to_kill)
 	__must_hold(&ctx->uring_lock)
 {
-	WARN_ON_ONCE(io_alloc_cache_empty(&ctx->rsrc_node_cache));
-	WARN_ON_ONCE(data_to_kill && !ctx->rsrc_node);
+	struct io_rsrc_node *node = ctx->rsrc_node;
+	struct io_rsrc_node *backup = io_rsrc_node_alloc(ctx);
 
-	if (data_to_kill) {
-		struct io_rsrc_node *rsrc_node = ctx->rsrc_node;
-
-		rsrc_node->rsrc_data = data_to_kill;
-		list_add_tail(&rsrc_node->node, &ctx->rsrc_ref_list);
-
-		data_to_kill->refs++;
-		/* put master ref */
-		io_put_rsrc_node(ctx, rsrc_node);
-		ctx->rsrc_node = NULL;
-	}
+	if (WARN_ON_ONCE(!backup))
+		return;
 
-	if (!ctx->rsrc_node)
-		ctx->rsrc_node = io_rsrc_node_alloc(ctx);
+	data_to_kill->refs++;
+	node->rsrc_data = data_to_kill;
+	list_add_tail(&node->node, &ctx->rsrc_ref_list);
+	/* put master ref */
+	io_put_rsrc_node(ctx, node);
+	ctx->rsrc_node = backup;
 }
 
 int io_rsrc_node_switch_start(struct io_ring_ctx *ctx)
@@ -921,9 +916,6 @@ int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 		return -EMFILE;
 	if (nr_args > rlimit(RLIMIT_NOFILE))
 		return -EMFILE;
-	ret = io_rsrc_node_switch_start(ctx);
-	if (ret)
-		return ret;
 	ret = io_rsrc_data_alloc(ctx, io_rsrc_file_put, tags, nr_args,
 				 &ctx->file_data);
 	if (ret)
@@ -978,7 +970,6 @@ int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 
 	/* default it to the whole table */
 	io_file_table_set_alloc_range(ctx, 0, ctx->nr_user_files);
-	io_rsrc_node_switch(ctx, NULL);
 	return 0;
 fail:
 	__io_sqe_files_unregister(ctx);
@@ -1260,9 +1251,6 @@ int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
 		return -EBUSY;
 	if (!nr_args || nr_args > IORING_MAX_REG_BUFFERS)
 		return -EINVAL;
-	ret = io_rsrc_node_switch_start(ctx);
-	if (ret)
-		return ret;
 	ret = io_rsrc_data_alloc(ctx, io_rsrc_buf_put, tags, nr_args, &data);
 	if (ret)
 		return ret;
@@ -1300,8 +1288,6 @@ int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
 	ctx->buf_data = data;
 	if (ret)
 		__io_sqe_buffers_unregister(ctx);
-	else
-		io_rsrc_node_switch(ctx, NULL);
 	return ret;
 }
 

io_uring/rsrc.h

@@ -74,6 +74,7 @@ void io_rsrc_put_work(struct work_struct *work);
 void io_wait_rsrc_data(struct io_rsrc_data *data);
 void io_rsrc_node_destroy(struct io_ring_ctx *ctx, struct io_rsrc_node *ref_node);
 int io_rsrc_node_switch_start(struct io_ring_ctx *ctx);
+struct io_rsrc_node *io_rsrc_node_alloc(struct io_ring_ctx *ctx);
 int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
 			  struct io_rsrc_node *node, void *rsrc);
 void io_rsrc_node_switch(struct io_ring_ctx *ctx,
@@ -164,6 +165,12 @@ static inline u64 *io_get_tag_slot(struct io_rsrc_data *data, unsigned int idx)
 	return &data->tags[table_idx][off];
 }
 
+static inline int io_rsrc_init(struct io_ring_ctx *ctx)
+{
+	ctx->rsrc_node = io_rsrc_node_alloc(ctx);
+	return ctx->rsrc_node ? 0 : -ENOMEM;
+}
+
 int io_files_update(struct io_kiocb *req, unsigned int issue_flags);
 int io_files_update_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);