FAILED: patch "[PATCH] io_uring: order refnode recycling" failed to apply to 5.9-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e297822b20e7fe683e107aea46e6402adcf99c70 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Wed, 18 Nov 2020 14:56:26 +0000
Subject: [PATCH] io_uring: order refnode recycling

Don't recycle a refnode until we're done with all requests of nodes
ejected before.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Cc: stable@vger.kernel.org # v5.7+
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5cb194ca4fce..7d4b755ab451 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -205,6 +205,7 @@ struct fixed_file_ref_node {
 	struct list_head		file_list;
 	struct fixed_file_data		*file_data;
 	struct llist_node		llist;
+	bool				done;
 };
 
 struct fixed_file_data {
@@ -7323,10 +7324,6 @@ static void __io_file_put_work(struct fixed_file_ref_node *ref_node)
 		kfree(pfile);
 	}
 
-	spin_lock(&file_data->lock);
-	list_del(&ref_node->node);
-	spin_unlock(&file_data->lock);
-
 	percpu_ref_exit(&ref_node->refs);
 	kfree(ref_node);
 	percpu_ref_put(&file_data->refs);
@@ -7353,17 +7350,32 @@ static void io_file_put_work(struct work_struct *work)
 static void io_file_data_ref_zero(struct percpu_ref *ref)
 {
 	struct fixed_file_ref_node *ref_node;
+	struct fixed_file_data *data;
 	struct io_ring_ctx *ctx;
-	bool first_add;
+	bool first_add = false;
 	int delay = HZ;
 
 	ref_node = container_of(ref, struct fixed_file_ref_node, refs);
-	ctx = ref_node->file_data->ctx;
+	data = ref_node->file_data;
+	ctx = data->ctx;
+
+	spin_lock(&data->lock);
+	ref_node->done = true;
+
+	while (!list_empty(&data->ref_list)) {
+		ref_node = list_first_entry(&data->ref_list,
+					struct fixed_file_ref_node, node);
+		/* recycle ref nodes in order */
+		if (!ref_node->done)
+			break;
+		list_del(&ref_node->node);
+		first_add |= llist_add(&ref_node->llist, &ctx->file_put_llist);
+	}
+	spin_unlock(&data->lock);
 
-	if (percpu_ref_is_dying(&ctx->file_data->refs))
+	if (percpu_ref_is_dying(&data->refs))
 		delay = 0;
 
-	first_add = llist_add(&ref_node->llist, &ctx->file_put_llist);
 	if (!delay)
 		mod_delayed_work(system_wq, &ctx->file_put_work, 0);
 	else if (first_add)
@@ -7387,6 +7399,7 @@ static struct fixed_file_ref_node *alloc_fixed_file_ref_node(
 	INIT_LIST_HEAD(&ref_node->node);
 	INIT_LIST_HEAD(&ref_node->file_list);
 	ref_node->file_data = ctx->file_data;
+	ref_node->done = false;
 	return ref_node;
 }
 
@@ -7482,7 +7495,7 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 
 	file_data->node = ref_node;
 	spin_lock(&file_data->lock);
-	list_add(&ref_node->node, &file_data->ref_list);
+	list_add_tail(&ref_node->node, &file_data->ref_list);
 	spin_unlock(&file_data->lock);
 	percpu_ref_get(&file_data->refs);
 	return ret;
@@ -7641,7 +7654,7 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 	if (needs_switch) {
 		percpu_ref_kill(&data->node->refs);
 		spin_lock(&data->lock);
-		list_add(&ref_node->node, &data->ref_list);
+		list_add_tail(&ref_node->node, &data->ref_list);
 		data->node = ref_node;
 		spin_unlock(&data->lock);
 		percpu_ref_get(&ctx->file_data->refs);