io_uring: preparation for rsrc tagging

We need a way to notify userspace when a lazily removed resource
actually died out. This will be done by associating a tag, which is u64
exactly like req->user_data, with each rsrc (e.g. buffer of file). A CQE
will be posted once a resource is actually put down.

Tag 0 is a special value set by default, for whcih it don't generate an
CQE, so providing the old behaviour.

Don't expose it to the userspace yet, but prepare internally, allocate
buffers, add all posting hooks, etc.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2e6beec5eabe7216bb61fb93cdf5aaf65812a9b0.1619356238.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -214,6 +214,7 @@ struct io_fixed_file {
 
 struct io_rsrc_put {
 	struct list_head list;
+	u64 tag;
 	union {
 		void *rsrc;
 		struct file *file;
@@ -239,6 +240,7 @@ typedef void (rsrc_put_fn)(struct io_ring_ctx *ctx, struct io_rsrc_put *prsrc);
 struct io_rsrc_data {
 	struct io_ring_ctx		*ctx;
 
+	u64				*tags;
 	rsrc_put_fn			*do_put;
 	atomic_t			refs;
 	struct completion		done;
@@ -7117,18 +7119,26 @@ static int io_rsrc_ref_quiesce(struct io_rsrc_data *data, struct io_ring_ctx *ct
 
 static void io_rsrc_data_free(struct io_rsrc_data *data)
 {
+	kvfree(data->tags);
 	kfree(data);
 }
 
 static struct io_rsrc_data *io_rsrc_data_alloc(struct io_ring_ctx *ctx,
-					       rsrc_put_fn *do_put)
+					       rsrc_put_fn *do_put,
+					       unsigned nr)
 {
 	struct io_rsrc_data *data;
 
 	data = kzalloc(sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return NULL;
 
+	data->tags = kvcalloc(nr, sizeof(*data->tags), GFP_KERNEL);
+	if (!data->tags) {
+		kfree(data);
+		return NULL;
+	}
+
 	atomic_set(&data->refs, 1);
 	data->ctx = ctx;
 	data->do_put = do_put;
@@ -7493,6 +7503,20 @@ static void __io_rsrc_put_work(struct io_rsrc_node *ref_node)
 
 	list_for_each_entry_safe(prsrc, tmp, &ref_node->rsrc_list, list) {
 		list_del(&prsrc->list);
+
+		if (prsrc->tag) {
+			bool lock_ring = ctx->flags & IORING_SETUP_IOPOLL;
+			unsigned long flags;
+
+			io_ring_submit_lock(ctx, lock_ring);
+			spin_lock_irqsave(&ctx->completion_lock, flags);
+			io_cqring_fill_event(ctx, prsrc->tag, 0, 0);
+			io_commit_cqring(ctx);
+			spin_unlock_irqrestore(&ctx->completion_lock, flags);
+			io_cqring_ev_posted(ctx);
+			io_ring_submit_unlock(ctx, lock_ring);
+		}
+
 		rsrc_data->do_put(ctx, prsrc);
 		kfree(prsrc);
 	}
@@ -7582,7 +7606,7 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 	if (ret)
 		return ret;
 
-	file_data = io_rsrc_data_alloc(ctx, io_rsrc_file_put);
+	file_data = io_rsrc_data_alloc(ctx, io_rsrc_file_put, nr_args);
 	if (!file_data)
 		return -ENOMEM;
 	ctx->file_data = file_data;
@@ -7683,7 +7707,7 @@ static int io_sqe_file_register(struct io_ring_ctx *ctx, struct file *file,
 #endif
 }
 
-static int io_queue_rsrc_removal(struct io_rsrc_data *data,
+static int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
 				 struct io_rsrc_node *node, void *rsrc)
 {
 	struct io_rsrc_put *prsrc;
@@ -7692,6 +7716,7 @@ static int io_queue_rsrc_removal(struct io_rsrc_data *data,
 	if (!prsrc)
 		return -ENOMEM;
 
+	prsrc->tag = data->tags[idx];
 	prsrc->rsrc = rsrc;
 	list_add(&prsrc->list, &node->rsrc_list);
 	return 0;
@@ -7732,7 +7757,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 
 		if (file_slot->file_ptr) {
 			file = (struct file *)(file_slot->file_ptr & FFS_MASK);
-			err = io_queue_rsrc_removal(data, ctx->rsrc_node, file);
+			err = io_queue_rsrc_removal(data, up->offset + done,
+						    ctx->rsrc_node, file);
 			if (err)
 				break;
 			file_slot->file_ptr = 0;