linux-kernel - Re: [PATCH] usb: dwc3: core: remove lock of otg mode during gadget suspend/resume to avoid deadlock

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Message-ID: <69839983-5ec0-4207-a798-8cdac7444f20@kernel.org>
Date: Thu, 13 Jun 2024 10:52:42 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Meng Li <Meng.Li@...driver.com>, Thinh.Nguyen@...opsys.com,
 gregkh@...uxfoundation.org, quic_uaggarwa@...cinc.com,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: dwc3: core: remove lock of otg mode during gadget
 suspend/resume to avoid deadlock

On 13/06/2024 09:23, Meng Li wrote:
> When config CONFIG_USB_DWC3_DUAL_ROLE is selected, and trigger system
> to enter suspend status with below command:
> echo mem > /sys/power/state
> There will be a deadlock issue occurring. Because dwc3_gadget_suspend() also
> try to get the lock again when previous invoked dwc3_suspend_common() has
> got the lock . This issue is introduced by commit c7ebd8149ee5 ("usb: dwc3:
> gadget: Fix NULL pointer dereference in dwc3_gadget_suspend") that removes
> the code of checking whether dwc->gadget_driver is NULL or not. It causes the
> following code is executed and deadlock occurs when trying to get the spinlock.
> To fix the deadlock issue, refer to commit 5265397f9442("usb: dwc3: Remove
> DWC3 locking during gadget suspend/resume"), remove lock of otg mode during
> gadget suspend/resume.

That's a funny way of fixing deadlocks: remove the lock. Of course it
could be correct way with some justification why locking is not needed.
No such justification here, so following your logic, let's remove
locking everywhere and then no deadlocks possible!

Let me prepare patches for that...

Best regards,
Krzysztof