linux-kernel - Re: [PATCH v1] Revert "tracing: Fix tracing_marker may trigger page fault during preempt

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Message-ID: <20251007154308.5b158d04@gandalf.local.home>
Date: Tue, 7 Oct 2025 15:43:08 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Runping Lai <runpinglai@...gle.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Wattson CI <wattson-external@...gle.com>,
 kernel-team@...roid.com, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, Luo Gengkun
 <luogengkun@...weicloud.com>, Linus Torvalds
 <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v1] Revert "tracing: Fix tracing_marker may trigger page
 fault during preempt_disable"

On Tue, 7 Oct 2025 11:19:34 -0700
Runping Lai <runpinglai@...gle.com> wrote:


> Hey Steve,
> 
> On Pixel6, CONFIG_PREEMPT is set. And CONFIG_PREEMPT_NONE
> is not set. I'll paste the full PREEMPT configs:

Hmm, now I'm curious to why _nofault() does't work but inatomic does.

> 
> >
> > The original code is buggy, but if this is causing a regression, then we
> > likely need to do something else, like copy in a pre-allocated buffer?  
> 
> Sounds like a good plan. Before the long term fix, can we please
> revert this commit?

Not that easy as the old way has a legitimate bug in it.

Could you see if adding pagefault_disable() and pagefault_enable() around
the __copy_from_user_inatomic() works for you? Or does that have the same
problem?

I do have a working solution, but it isn't trivial.

-- Steve