linux-kernel - Re: [PATCH] tracing: wprobe: Fix to use IS_ERR

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Message-Id: <20251007093510.bbc8b59c21195973e740ea7a@kernel.org>
Date: Tue, 7 Oct 2025 09:35:10 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, Mark Brown <broonie@...nel.org>,
 Menglong Dong <menglong8.dong@...il.com>, Thorsten Blum
 <thorsten.blum@...ux.dev>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: wprobe: Fix to use IS_ERR_PCPU() for per-cpu
 pointer

On Mon, 6 Oct 2025 11:06:31 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Mon, 6 Oct 2025 at 02:47, Masami Hiramatsu (Google)
> <mhiramat@...nel.org> wrote:
> >
> >         tw->bp_event = register_wide_hw_breakpoint(&attr, wprobe_perf_handler, tw);
> > -       if (IS_ERR((void * __force)tw->bp_event)) {
> > +       if (IS_ERR_PCPU((void * __force)tw->bp_event)) {
> >                 int ret = PTR_ERR((void * __force)tw->bp_event);
> 
> No, this is still entirely wrong.
> 
> That casts are *WRONG*. They should not exist. And they will cause
> compiler errors, because you are casting fundamentally different
> pointer types.

Ah, got it!

> 
> They don't just point to different types, they aren't even in the same
> address space!
> 
> Stop adding random casts. They are a sign of type errors, and as long
> as they are there, the code is buggy.

OK.

> 
> And no, it's not just that IS_ERR() that was wrong. That PTR_ERR()
> won't work on a percpu pointer either.
> 
> No more of this randomness, please.

OK, let me fix that.

Thank you!


> 
>                Linus


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>