Re: [PATCH v5 12/20] vsprintf: add new `%pA` format specifier

From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Petr Mladek <pmladek@suse.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Miguel Ojeda <ojeda@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
	Gary Guo <gary@garyguo.net>, Alex Gaynor <alex.gaynor@gmail.com>,
	Wedson Almeida Filho <wedsonaf@google.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>
Subject: Re: [PATCH v5 12/20] vsprintf: add new `%pA` format specifier
Date: Tue, 22 Mar 2022 13:16:54 +0900	[thread overview]
Message-ID: <YjlNtkNP1FJ4XEyX@google.com> (raw)
In-Reply-To: <YjStnb7nNTC3kYw6@alley>

On (22/03/18 17:04), Petr Mladek wrote:
> On Fri 2022-03-18 16:07:31, Andy Shevchenko wrote:
> > On Thu, Mar 17, 2022 at 07:10:00PM +0100, Miguel Ojeda wrote:
> > > From: Gary Guo <gary@garyguo.net>
> > > +	case 'A':
> > > +		if (!IS_ENABLED(CONFIG_RUST)) {
> > > +			WARN_ONCE(1, "Please remove %%pA from non-Rust code\n");
> > > +			return error_string(buf, end, "(%pA?)", spec);
> > > +		}
> > 
> > I'm wondering if the Big Scary Banner as trace_printk() does would be better
> > (in case we can tell that %pA is used in the code when RUST=n).
> 
> Good question!
> 
> The advantage of WARN_ONCE() is that it shows the stack so that it is
> easier to locate the caller.
> 
> On the other hand, WARN_ONCE() is a bit misused here. It should be
> used only in situations that might be potentially fatal. It might
> even cause panic() with "panic_on_warn" kernel parameter.

Stack trace is certainly helpful here. So maybe dump_stack() instead
of WARN_ONCE()? I guess I don't mind WARN_ONCE().