linux-kernel - Re: [PATCH v3 0/4] kcov, usb: Fix invalid context sleep in softirq path on PREEMPT

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Message-ID: <20250804122405.3e9d83ed@gandalf.local.home>
Date: Mon, 4 Aug 2025 12:24:05 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Yunseong Kim <ysk@...lloc.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>, Andrey Konovalov
 <andreyknvl@...il.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Thomas Gleixner <tglx@...utronix.de>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>, Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
 Byungchul Park <byungchul@...com>, max.byungchul.park@...il.com, Yeoreum
 Yun <yeoreum.yun@....com>, ppbuk5246@...il.com, linux-usb@...r.kernel.org,
 linux-rt-devel@...ts.linux.dev, syzkaller@...glegroups.com,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3 0/4] kcov, usb: Fix invalid context sleep in softirq
 path on PREEMPT_RT

On Sun,  3 Aug 2025 07:20:41 +0000
Yunseong Kim <ysk@...lloc.com> wrote:

> This patch series resolves a sleeping function called from invalid context
> bug that occurs when fuzzing USB with syzkaller on a PREEMPT_RT kernel.
> 
> The regression was introduced by the interaction of two separate patches:
> one that made kcov's internal locks sleep on PREEMPT_RT for better latency

Just so I fully understand this change. It is basically reverting the
"better latency" changes? That is, with KCOV anyone running with PREEMPT_RT
can expect non deterministic latency behavior?

This should be fully documented. I assume this will not be a problem as
kcov is more for debugging and should not be enabled in production.

-- Steve