# Re: \[PATCH v8 10/12\] unwind\_user/sframe: Enable debugging in uaccess regions

- From: Josh Poimboeuf \<jpoimboe@kernel.org\>
- Date: 2025-07-08 18:57:07 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2025/07/3126078
- Thread: https://ratatoskr.run/linux-trace-kernel/2025/07/3124692/t.md

```text
On Tue, Jul 08, 2025 at 12:31:20PM -0400, Steven Rostedt wrote:
> On Tue, 8 Jul 2025 08:53:56 -0700
> Linus Torvalds [ref] wrote:
> 
> > On Tue, 8 Jul 2025 at 07:41, Steven Rostedt [ref] wrote:
> > >
> > > Would something like this work? If someone enables the config to enable the
> > > validation, I don't think we need dynamic printk to do it (as that requires
> > > passing in the format directly and not via a pointer).  
> > 
> > I really think you should just not use 'user_access_begin()" AT ALL if
> > you need to play these kinds of games.
> > 
> 
> Looking at the code a bit deeper, I don't think we need to play these games
> and still keep the user_read_access_begin().
> 
> The places that are more performance critical (where it reads the sframe
> during normal stack walking during profiling) has no debug output, and
> there's nothing there that needs to take it out of the user_read_access
> area.
> 
> It's the validator that adds these hacks. I don't think it needs to. It can
> just wrap the calls to the code that requires user_read_access and then
> check the return value. The validator is just a debugging feature and
> performance should not be an issue.
> 
> But I do think performance is something to care about during normal
> operations where the one big user_read_access_begin() can help.
> 
> What about something like this? It adds "safe" versions of the user space
> access functions and uses them only in the slow (we don't care about
> performance) validator:

Looks good to me, thanks!

-- 
Josh
```