linux-kernel - [PATCH 2/2] usb: gadget: uvc: Remove nested locking

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Message-ID: <20231215210746.821494-2-arakesh@google.com>
Date: Fri, 15 Dec 2023 13:07:45 -0800
From: Avichal Rakesh <arakesh@...gle.com>
To: dan.scally@...asonboard.com, gregkh@...uxfoundation.org, 
	laurent.pinchart@...asonboard.com
Cc: etalvala@...gle.com, jchowdhary@...gle.com, linux-kernel@...r.kernel.org, 
	linux-usb@...r.kernel.org, Avichal Rakesh <arakesh@...gle.com>
Subject: [PATCH 2/2] usb: gadget: uvc: Remove nested locking

When handling error status from uvcg_video_usb_req_queue,
uvc_video_complete currently calls uvcg_queue_cancel with
video->req_lock held. uvcg_queue_cancel internally locks
queue->irqlock, which nests queue->irqlock inside
video->req_lock. This isn't a functional bug at the
moment, but does open up possibilities for ABBA
deadlocks in the future.

This patch fixes the accidental nesting by dropping
video->req_lock before calling uvcg_queue_cancel.

Signed-off-by: Avichal Rakesh <arakesh@...gle.com>
---
 drivers/usb/gadget/function/uvc_video.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index e5db1be14ca3..d15b9b4c4fcc 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -469,13 +469,15 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req)
 			 * Put request back in req_free for it to be cleaned
 			 * up later.
 			 */
-			uvcg_queue_cancel(queue, 0);
 			list_add_tail(&to_queue->list, &video->req_free);
 		}
 	} else {
 		uvc_video_free_request(ureq, ep);
+		ret = 0;
 	}
 	spin_unlock_irqrestore(&video->req_lock, flags);
+	if (ret < 0)
+		uvcg_queue_cancel(queue, 0);
 }
 
 static int
-- 
2.43.0.472.g3155946c3a-goog