FAILED: patch "[PATCH] usb: gadget: f_hid: move list and spinlock inits from bind to" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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 <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 4e0a88254ad59f6c53a34bf5fa241884ec09e8b2
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026040826-pagan-amuser-3732@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 4e0a88254ad59f6c53a34bf5fa241884ec09e8b2 Mon Sep 17 00:00:00 2001
From: Michael Zimmermann <[email protected]>
Date: Tue, 31 Mar 2026 20:48:44 +0200
Subject: [PATCH] usb: gadget: f_hid: move list and spinlock inits from bind to
alloc

There was an issue when you did the following:
- setup and bind an hid gadget
- open /dev/hidg0
- use the resulting fd in EPOLL_CTL_ADD
- unbind the UDC
- bind the UDC
- use the fd in EPOLL_CTL_DEL

When CONFIG_DEBUG_LIST was enabled, a list_del corruption was reported within remove_wait_queue (via ep_remove_wait_queue). After some debugging I found out that the queues, which f_hid registers via poll_wait were the problem. These were initialized using init_waitqueue_head inside hidg_bind. So effectively, the bind function re-initialized the queues while there were still items in them.

The solution is to move the initialization from hidg_bind to hidg_alloc to extend their lifetimes to the lifetime of the function instance.

Additionally, I found many other possibly problematic init calls in the bind function, which I moved as well.

index 8812ebf33d14..e5ccaec7750c 100644
@@ -1262,17 +1262,8 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
 	if (status)
 		goto fail;
 
-	spin_lock_init(&hidg->write_spinlock);
 	hidg->write_pending = 1;
 	hidg->req = NULL;
-	spin_lock_init(&hidg->read_spinlock);
-	spin_lock_init(&hidg->get_report_spinlock);
-	init_waitqueue_head(&hidg->write_queue);
-	init_waitqueue_head(&hidg->read_queue);
-	init_waitqueue_head(&hidg->get_queue);
-	init_waitqueue_head(&hidg->get_id_queue);
-	INIT_LIST_HEAD(&hidg->completed_out_req);
-	INIT_LIST_HEAD(&hidg->report_list);
 
 	INIT_WORK(&hidg->work, get_report_workqueue_handler);
 	hidg->workqueue = alloc_workqueue("report_work",

@@ -1608,6 +1599,16 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
 
 	mutex_lock(&opts->lock);
 
+	spin_lock_init(&hidg->write_spinlock);
+	spin_lock_init(&hidg->read_spinlock);
+	spin_lock_init(&hidg->get_report_spinlock);
+	init_waitqueue_head(&hidg->write_queue);
+	init_waitqueue_head(&hidg->read_queue);
+	init_waitqueue_head(&hidg->get_queue);
+	init_waitqueue_head(&hidg->get_id_queue);
+	INIT_LIST_HEAD(&hidg->completed_out_req);
+	INIT_LIST_HEAD(&hidg->report_list);
+
 	device_initialize(&hidg->dev);
 	hidg->dev.release = hidg_release;
 	hidg->dev.class = &hidg_class;

From: Michael Zimmermann <[email protected]>

[ Upstream commit 4e0a88254ad59f6c53a34bf5fa241884ec09e8b2 ]

There was an issue when you did the following:
- setup and bind an hid gadget
- open /dev/hidg0
- use the resulting fd in EPOLL_CTL_ADD
- unbind the UDC
- bind the UDC
- use the fd in EPOLL_CTL_DEL

When CONFIG_DEBUG_LIST was enabled, a list_del corruption was reported within remove_wait_queue (via ep_remove_wait_queue). After some debugging I found out that the queues, which f_hid registers via poll_wait were the problem. These were initialized using init_waitqueue_head inside hidg_bind. So effectively, the bind function re-initialized the queues while there were still items in them.

The solution is to move the initialization from hidg_bind to hidg_alloc to extend their lifetimes to the lifetime of the function instance.

Additionally, I found many other possibly problematic init calls in the bind function, which I moved as well.

---
 drivers/usb/gadget/function/f_hid.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

index d8dafebeabea4..2137513b23a08 100644
@@ -1000,13 +1000,8 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
 	if (status)
 		goto fail;
 
-	spin_lock_init(&hidg->write_spinlock);
 	hidg->write_pending = 1;
 	hidg->req = NULL;
-	spin_lock_init(&hidg->read_spinlock);
-	init_waitqueue_head(&hidg->write_queue);
-	init_waitqueue_head(&hidg->read_queue);
-	INIT_LIST_HEAD(&hidg->completed_out_req);
 
 	/* create char device */
 	cdev_init(&hidg->cdev, &f_hidg_fops);

@@ -1275,6 +1270,12 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
 
 	mutex_lock(&opts->lock);
 
+	spin_lock_init(&hidg->write_spinlock);
+	spin_lock_init(&hidg->read_spinlock);
+	init_waitqueue_head(&hidg->write_queue);
+	init_waitqueue_head(&hidg->read_queue);
+	INIT_LIST_HEAD(&hidg->completed_out_req);
+
 	device_initialize(&hidg->dev);
 	hidg->dev.release = hidg_release;
 	hidg->dev.class = &hidg_class;

2.53.0