linux-kernel - Re: [PATCH] usb: mon: Make mon

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Message-ID: <4f7805f7-805a-4678-8844-c38a97650dda@rowland.harvard.edu>
Date: Mon, 15 Sep 2025 10:19:55 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Lizhi Xu <lizhi.xu@...driver.com>
Cc: syzbot+205ef33a3b636b4181fb@...kaller.appspotmail.com,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] usb: mon: Make mon_bus::lock a raw spinlock

On Mon, Sep 15, 2025 at 09:29:13AM +0800, Lizhi Xu wrote:
> Interrupts are disabled before entering usb_hcd_giveback_urb().

This needs to be fixed in the usbip driver.  There is no need to change 
usbmon.

> A spinlock_t becomes a sleeping lock on PREEMPT_RT, so it cannot be
> acquired with disabled interrupts.
> 
> Make mon_bus::lock a raw spinlock so it can be used with interrupts disabled.

See commit 8d63c83d8eb9 ("USB: gadget: dummy-hcd: Fix locking bug in 
RT-enabled kernels") for an example of how to avoid disabling 
interrupts before calling usb_hcd_giveback_urb().

Alan Stern