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

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Message-ID: <aLVqyEGoHKVCFGFR@J2N7QTR9R3>
Date: Mon, 1 Sep 2025 10:43:36 +0100
From: Mark Rutland <mark.rutland@....com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Luo Gengkun <luogengkun@...weicloud.com>, mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] tracing: Fix tracing_marker may trigger page fault
 during preempt_disable

On Fri, Aug 29, 2025 at 06:13:11PM -0400, Steven Rostedt wrote:
> On Fri, 29 Aug 2025 20:53:40 +0100
> Catalin Marinas <catalin.marinas@....com> wrote:
> valid user address.
> > 
> > BTW, arm64 also bails out early in do_page_fault() if in_atomic() but I
> > suspect that's not the case here.
> > 
> > Adding Al Viro since since he wrote a large part of uaccess.h.
> > 
> 
> So, __copy_from_user_inatomic() is supposed to be called if
> pagefault_disable() has already been called? If this is the case, can we
> add more comments to this code?

Just to check, you're asking for better comments in <linux/uaccess.h>,
right?

> I've been using the inatomic() version this
> way in preempt disabled locations since 2016.
> 
> Looks like it needs to be converted to copy_from_user_nofault().
> 
> Luo, this version of the patch looks legit, no need for a v2.
> 
> I just wanted to figure out why __copy_from_user_inatomic() wasn't atomic.
> If anything, it needs to be better documented.

If that had roughly the same kerneldoc comment as for
__copy_to_user_inatomic(), would that be sufficient, or do you think
both need to be made more explicit?

Mark.