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From:   Dan Vacura <w36195@motorola.com>
To:     linux-usb@vger.kernel.org
Cc:     Dan Vacura <w36195@motorola.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Felipe Balbi <balbi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Subject: [PATCH] usb: gadget: uvc: allow for application to cleanly shutdown
Date:   Fri, 29 Apr 2022 14:20:01 -0500
Message-Id: <20220429192001.385636-1-w36195@motorola.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Several types of kernel panics can occur due to timing during the uvc
gadget removal. This appears to be a problem with gadget resources being
managed by both the client application's v4l2 open/close and the UDC
gadget bind/unbind. Since the concept of USB_GADGET_DELAYED_STATUS
doesn't exist for unbind, add a wait to allow for the application to
close out.

Some examples of the panics that can occur are:

<1>[ 1147.652313] Unable to handle kernel NULL pointer dereference at
virtual address 0000000000000028
<4>[ 1147.652510] Call trace:
<4>[ 1147.652514]  usb_gadget_disconnect+0x74/0x1f0
<4>[ 1147.652516]  usb_gadget_deactivate+0x38/0x168
<4>[ 1147.652520]  usb_function_deactivate+0x54/0x90
<4>[ 1147.652524]  uvc_function_disconnect+0x14/0x38
<4>[ 1147.652527]  uvc_v4l2_release+0x34/0xa0
<4>[ 1147.652537]  __fput+0xdc/0x2c0
<4>[ 1147.652540]  ____fput+0x10/0x1c
<4>[ 1147.652545]  task_work_run+0xe4/0x12c
<4>[ 1147.652549]  do_notify_resume+0x108/0x168

<1>[  282.950561][ T1472] Unable to handle kernel NULL pointer
dereference at virtual address 00000000000005b8
<6>[  282.953111][ T1472] Call trace:
<6>[  282.953121][ T1472]  usb_function_deactivate+0x54/0xd4
<6>[  282.953134][ T1472]  uvc_v4l2_release+0xac/0x1e4
<6>[  282.953145][ T1472]  v4l2_release+0x134/0x1f0
<6>[  282.953167][ T1472]  __fput+0xf4/0x428
<6>[  282.953178][ T1472]  ____fput+0x14/0x24
<6>[  282.953193][ T1472]  task_work_run+0xac/0x130

<3>[  213.410077][   T29] configfs-gadget gadget: uvc: Failed to queue
request (-108).
<1>[  213.410116][   T29] Unable to handle kernel NULL pointer
dereference at virtual address 0000000000000003
<6>[  213.413460][   T29] Call trace:
<6>[  213.413474][   T29]  uvcg_video_pump+0x1f0/0x384
<6>[  213.413489][   T29]  process_one_work+0x2a4/0x544
<6>[  213.413502][   T29]  worker_thread+0x350/0x784
<6>[  213.413515][   T29]  kthread+0x2ac/0x320
<6>[  213.413528][   T29]  ret_from_fork+0x10/0x30

Signed-off-by: Dan Vacura <w36195@motorola.com>
---
 drivers/usb/gadget/function/f_uvc.c    | 24 ++++++++++++++++++++++++
 drivers/usb/gadget/function/uvc.h      |  2 ++
 drivers/usb/gadget/function/uvc_v4l2.c |  3 ++-
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
index 50e6e7a58b41..3cc8cf24a7c7 100644
--- a/drivers/usb/gadget/function/f_uvc.c
+++ b/drivers/usb/gadget/function/f_uvc.c
@@ -892,13 +892,36 @@ static void uvc_function_unbind(struct usb_configuration *c,
 {
 	struct usb_composite_dev *cdev = c->cdev;
 	struct uvc_device *uvc = to_uvc(f);
+	int wait_ret = 1;
 
 	uvcg_info(f, "%s()\n", __func__);
 
+	/* If we know we're connected via v4l2, then there should be a cleanup
+	 * of the device from userspace either via UVC_EVENT_DISCONNECT or
+	 * though the video device removal uevent. Allow some time for the
+	 * application to close out before things get deleted.
+	 */
+	if (uvc->func_connected) {
+		uvcg_info(f, "%s waiting for clean disconnect\n", __func__);
+		wait_ret = wait_event_interruptible_timeout(uvc->func_connected_queue,
+				uvc->func_connected == false, msecs_to_jiffies(500));
+		uvcg_info(f, "%s done waiting with ret: %u\n", __func__, wait_ret);
+	}
+
 	device_remove_file(&uvc->vdev.dev, &dev_attr_function_name);
 	video_unregister_device(&uvc->vdev);
 	v4l2_device_unregister(&uvc->v4l2_dev);
 
+	if (uvc->func_connected) {
+		/* Wait for the release to occur to ensure there are no longer any
+		 * pending operations that may cause panics when resources are cleaned
+		 * up.
+		 */
+		uvcg_warn(f, "%s no clean disconnect, wait for release\n", __func__);
+		wait_ret = wait_event_interruptible_timeout(uvc->func_connected_queue,
+				uvc->func_connected == false, msecs_to_jiffies(1000));
+	}
+
 	usb_ep_free_request(cdev->gadget->ep0, uvc->control_req);
 	kfree(uvc->control_buf);
 
@@ -917,6 +940,7 @@ static struct usb_function *uvc_alloc(struct usb_function_instance *fi)
 
 	mutex_init(&uvc->video.mutex);
 	uvc->state = UVC_STATE_DISCONNECTED;
+	init_waitqueue_head(&uvc->func_connected_queue);
 	opts = fi_to_f_uvc_opts(fi);
 
 	mutex_lock(&opts->lock);
diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
index 9eec104b3666..58e383afdd44 100644
--- a/drivers/usb/gadget/function/uvc.h
+++ b/drivers/usb/gadget/function/uvc.h
@@ -14,6 +14,7 @@
 #include <linux/spinlock.h>
 #include <linux/usb/composite.h>
 #include <linux/videodev2.h>
+#include <linux/wait.h>
 
 #include <media/v4l2-device.h>
 #include <media/v4l2-dev.h>
@@ -130,6 +131,7 @@ struct uvc_device {
 	struct usb_function func;
 	struct uvc_video video;
 	bool func_connected;
+	wait_queue_head_t func_connected_queue;
 
 	/* Descriptors */
 	struct {
diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c
index a2c78690c5c2..fd8f73bb726d 100644
--- a/drivers/usb/gadget/function/uvc_v4l2.c
+++ b/drivers/usb/gadget/function/uvc_v4l2.c
@@ -253,10 +253,11 @@ uvc_v4l2_subscribe_event(struct v4l2_fh *fh,
 
 static void uvc_v4l2_disable(struct uvc_device *uvc)
 {
-	uvc->func_connected = false;
 	uvc_function_disconnect(uvc);
 	uvcg_video_enable(&uvc->video, 0);
 	uvcg_free_buffers(&uvc->video.queue);
+	uvc->func_connected = false;
+	wake_up_interruptible(&uvc->func_connected_queue);
 }
 
 static int
-- 
2.32.0