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

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Message-ID: <20250829181311.079f33bf@gandalf.local.home>
Date: Fri, 29 Aug 2025 18:13:11 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Catalin Marinas <catalin.marinas@....com>
Cc: 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, Mark Rutland <mark.rutland@....com>,
 Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] tracing: Fix tracing_marker may trigger page fault
 during preempt_disable

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? 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.

-- Steve