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

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Message-ID: <CABgk4RSxm8mNJcRn0HdNH3+Y=VDL5gNVvyhhR26wjBme+i5X-g@mail.gmail.com>
Date: Tue, 7 Oct 2025 16:25:41 -0700
From: Runping Lai <runpinglai@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>
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, Oct 7, 2025 at 2:40 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 7 Oct 2025 16:31:41 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
>
> > +static void trace_user_fault_buffer_free(struct trace_user_buf_info *tinfo)
> > +{
> > +     char *buf;
> > +     int cpu;
> > +
> > +     for_each_possible_cpu(cpu) {
> > +             buf = per_cpu_ptr(tinfo->tbuf, cpu)->buf;
> > +             kfree(buf);
> > +     }
>
> Oops, missed:
>
>         free_percpu(tinfo->tbuf);
>
> here.

Hey Steve,

Thanks for providing the buffer-based solution. I tried it and it
fixes the problem!
However, the first experiment, adding pagefault_disable/enable()
around copy_nofault()
doesn't help. Still having the same problem. I suppose the issue is
more than pagefault?

Can you please suggest the next move? I can also do more tests if needed.

Best,
Runping

>
> -- Steve
>
> > +     kfree(tinfo);
> > +}