io_uring: introduce ctx to tctx back map

For each pair tcxt-ctx create an object and chain it into ctx, so we
have a way to traverse all tctx that are using current ctx. Preparation
patch, will be used later.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -454,6 +454,7 @@ struct io_ring_ctx {
 
 	/* Keep this last, we don't need it for the fast path */
 	struct work_struct		exit_work;
+	struct list_head		tctx_list;
 };
 
 /*
@@ -805,6 +806,13 @@ struct io_kiocb {
 	struct io_wq_work		work;
 };
 
+struct io_tctx_node {
+	struct list_head	ctx_node;
+	struct task_struct	*task;
+	struct file		*file;
+	struct io_ring_ctx	*ctx;
+};
+
 struct io_defer_entry {
 	struct list_head	list;
 	struct io_kiocb		*req;
@@ -1144,6 +1152,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	INIT_LIST_HEAD(&ctx->rsrc_ref_list);
 	INIT_DELAYED_WORK(&ctx->rsrc_put_work, io_rsrc_put_work);
 	init_llist_head(&ctx->rsrc_put_llist);
+	INIT_LIST_HEAD(&ctx->tctx_list);
 	INIT_LIST_HEAD(&ctx->submit_state.comp.free_list);
 	INIT_LIST_HEAD(&ctx->submit_state.comp.locked_free_list);
 	return ctx;
@@ -8748,6 +8757,7 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
 static int io_uring_add_task_file(struct io_ring_ctx *ctx, struct file *file)
 {
 	struct io_uring_task *tctx = current->io_uring;
+	struct io_tctx_node *node;
 	int ret;
 
 	if (unlikely(!tctx)) {
@@ -8760,13 +8770,25 @@ static int io_uring_add_task_file(struct io_ring_ctx *ctx, struct file *file)
 		void *old = xa_load(&tctx->xa, (unsigned long)file);
 
 		if (!old) {
+			node = kmalloc(sizeof(*node), GFP_KERNEL);
+			if (!node)
+				return -ENOMEM;
+			node->ctx = ctx;
+			node->file = file;
+			node->task = current;
+
 			get_file(file);
 			ret = xa_err(xa_store(&tctx->xa, (unsigned long)file,
-						file, GFP_KERNEL));
+						node, GFP_KERNEL));
 			if (ret) {
 				fput(file);
+				kfree(node);
 				return ret;
 			}
+
+			mutex_lock(&ctx->uring_lock);
+			list_add(&node->ctx_node, &ctx->tctx_list);
+			mutex_unlock(&ctx->uring_lock);
 		}
 		tctx->last = file;
 	}
@@ -8788,23 +8810,31 @@ static int io_uring_add_task_file(struct io_ring_ctx *ctx, struct file *file)
 static void io_uring_del_task_file(unsigned long index)
 {
 	struct io_uring_task *tctx = current->io_uring;
-	struct file *file;
+	struct io_tctx_node *node;
 
-	file = xa_erase(&tctx->xa, index);
-	if (!file)
+	node = xa_erase(&tctx->xa, index);
+	if (!node)
 		return;
 
-	if (tctx->last == file)
+	WARN_ON_ONCE(current != node->task);
+	WARN_ON_ONCE(list_empty(&node->ctx_node));
+
+	mutex_lock(&node->ctx->uring_lock);
+	list_del(&node->ctx_node);
+	mutex_unlock(&node->ctx->uring_lock);
+
+	if (tctx->last == node->file)
 		tctx->last = NULL;
-	fput(file);
+	fput(node->file);
+	kfree(node);
 }
 
 static void io_uring_clean_tctx(struct io_uring_task *tctx)
 {
-	struct file *file;
+	struct io_tctx_node *node;
 	unsigned long index;
 
-	xa_for_each(&tctx->xa, index, file)
+	xa_for_each(&tctx->xa, index, node)
 		io_uring_del_task_file(index);
 	if (tctx->io_wq) {
 		io_wq_put_and_exit(tctx->io_wq);
@@ -8815,13 +8845,13 @@ static void io_uring_clean_tctx(struct io_uring_task *tctx)
 void __io_uring_files_cancel(struct files_struct *files)
 {
 	struct io_uring_task *tctx = current->io_uring;
-	struct file *file;
+	struct io_tctx_node *node;
 	unsigned long index;
 
 	/* make sure overflow events are dropped */
 	atomic_inc(&tctx->in_idle);
-	xa_for_each(&tctx->xa, index, file)
-		io_uring_cancel_task_requests(file->private_data, files);
+	xa_for_each(&tctx->xa, index, node)
+		io_uring_cancel_task_requests(node->ctx, files);
 	atomic_dec(&tctx->in_idle);
 
 	if (files)
@@ -8884,11 +8914,11 @@ void __io_uring_task_cancel(void)
 	atomic_inc(&tctx->in_idle);
 
 	if (tctx->sqpoll) {
-		struct file *file;
+		struct io_tctx_node *node;
 		unsigned long index;
 
-		xa_for_each(&tctx->xa, index, file)
-			io_uring_cancel_sqpoll(file->private_data);
+		xa_for_each(&tctx->xa, index, node)
+			io_uring_cancel_sqpoll(node->ctx);
 	}
 
 	do {