io_uring: index io_uring->xa by ctx not file

We don't use task file notes anymore, and no need left in indexing
task->io_uring->xa by file, and replace it with ctx. It's better
design-wise, especially since we keep a dangling file, and so have to
keep an eye on not dereferencing it.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -809,7 +809,6 @@ struct io_kiocb {
 struct io_tctx_node {
 	struct list_head	ctx_node;
 	struct task_struct	*task;
-	struct file		*file;
 	struct io_ring_ctx	*ctx;
 };
 
@@ -8540,7 +8539,7 @@ static bool io_run_ctx_fallback(struct io_ring_ctx *ctx)
 struct io_tctx_exit {
 	struct callback_head		task_work;
 	struct completion		completion;
-	unsigned long			index;
+	struct io_ring_ctx		*ctx;
 };
 
 static void io_tctx_exit_cb(struct callback_head *cb)
@@ -8554,7 +8553,7 @@ static void io_tctx_exit_cb(struct callback_head *cb)
 	 * node. It'll be removed by the end of cancellation, just ignore it.
 	 */
 	if (!atomic_read(&tctx->in_idle))
-		io_uring_del_task_file(work->index);
+		io_uring_del_task_file((unsigned long)work->ctx);
 	complete(&work->completion);
 }
 
@@ -8579,7 +8578,7 @@ static void io_ring_exit_work(struct work_struct *work)
 	while (!list_empty(&ctx->tctx_list)) {
 		node = list_first_entry(&ctx->tctx_list, struct io_tctx_node,
 					ctx_node);
-		exit.index = (unsigned long)node->file;
+		exit.ctx = ctx;
 		init_completion(&exit.completion);
 		init_task_work(&exit.task_work, io_tctx_exit_cb);
 		ret = task_work_add(node->task, &exit.task_work, TWA_SIGNAL);
@@ -8798,7 +8797,7 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
 /*
  * Note that this task has used io_uring. We use it for cancelation purposes.
  */
-static int io_uring_add_task_file(struct io_ring_ctx *ctx, struct file *file)
+static int io_uring_add_task_file(struct io_ring_ctx *ctx)
 {
 	struct io_uring_task *tctx = current->io_uring;
 	struct io_tctx_node *node;
@@ -8810,18 +8809,17 @@ static int io_uring_add_task_file(struct io_ring_ctx *ctx, struct file *file)
 			return ret;
 		tctx = current->io_uring;
 	}
-	if (tctx->last != file) {
-		void *old = xa_load(&tctx->xa, (unsigned long)file);
+	if (tctx->last != ctx) {
+		void *old = xa_load(&tctx->xa, (unsigned long)ctx);
 
 		if (!old) {
 			node = kmalloc(sizeof(*node), GFP_KERNEL);
 			if (!node)
 				return -ENOMEM;
 			node->ctx = ctx;
-			node->file = file;
 			node->task = current;
 
-			ret = xa_err(xa_store(&tctx->xa, (unsigned long)file,
+			ret = xa_err(xa_store(&tctx->xa, (unsigned long)ctx,
 						node, GFP_KERNEL));
 			if (ret) {
 				kfree(node);
@@ -8832,7 +8830,7 @@ static int io_uring_add_task_file(struct io_ring_ctx *ctx, struct file *file)
 			list_add(&node->ctx_node, &ctx->tctx_list);
 			mutex_unlock(&ctx->uring_lock);
 		}
-		tctx->last = file;
+		tctx->last = ctx;
 	}
 
 	/*
@@ -8867,7 +8865,7 @@ static void io_uring_del_task_file(unsigned long index)
 	list_del(&node->ctx_node);
 	mutex_unlock(&node->ctx->uring_lock);
 
-	if (tctx->last == node->file)
+	if (tctx->last == node->ctx)
 		tctx->last = NULL;
 	kfree(node);
 }
@@ -9166,7 +9164,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 		}
 		submitted = to_submit;
 	} else if (to_submit) {
-		ret = io_uring_add_task_file(ctx, f.file);
+		ret = io_uring_add_task_file(ctx);
 		if (unlikely(ret))
 			goto out;
 		mutex_lock(&ctx->uring_lock);
@@ -9375,7 +9373,7 @@ static int io_uring_install_fd(struct io_ring_ctx *ctx, struct file *file)
 	if (fd < 0)
 		return fd;
 
-	ret = io_uring_add_task_file(ctx, file);
+	ret = io_uring_add_task_file(ctx);
 	if (ret) {
 		put_unused_fd(fd);
 		return ret;

include/linux/io_uring.h

@@ -18,7 +18,7 @@ struct io_uring_task {
 	/* submission side */
 	struct xarray		xa;
 	struct wait_queue_head	wait;
-	struct file		*last;
+	void			*last;
 	void			*io_wq;
 	struct percpu_counter	inflight;
 	atomic_t		in_idle;