linux-kernel - Re: [BUG] usb: sleepable spinlock used in USB bh_worker softirq on PREEMPT

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Message-ID: <20250811091559.CXIs7FvU@linutronix.de>
Date: Mon, 11 Aug 2025 11:15:59 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Yunseong Kim <ysk@...lloc.com>
Cc: linux-usb@...r.kernel.org, linux-rt-users@...r.kernel.org,
	gregkh@...uxfoundation.org, stern@...land.harvard.edu,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	syzkaller@...glegroups.com
Subject: Re: [BUG] usb: sleepable spinlock used in USB bh_worker softirq on
 PREEMPT_RT

On 2025-08-11 00:05:49 [+0900], Yunseong Kim wrote:
> While running a PREEMPT_RT-enabled kernel I observed a sleepable
> spinlock (rt_spin_lock) being taken from a softirq context within
> the USB core framework. On PREEMPT_RT, spin_lock() may sleep when
> contended. This is unsafe in softirq context and can cause hangs or
> deadlocks.
> 
…
> I believe this requires a change in the USB core framework rather than
> just in individual drivers.
> 
> Kernel config, full logs, and reproduction steps can be provided on
> request.
> 
> This bug was uncovered during my work to fixing KCOV for PREEMPT_RT awareness.
> Link: https://lore.kernel.org/all/ee26e7b2-80dd-49b1-bca2-61e460f73c2d@kzalloc.com/t/#u

I'm confused. Is this new or this the same bug that was reported by you
in the thread you linked?
The kcov issue should be fixed by
	https://lore.kernel.org/all/20250811082745.ycJqBXMs@linutronix.de/

> Best Regards,
> Yunseong Kim

Sebastian