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

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Message-ID: <YjlNtkNP1FJ4XEyX@google.com>
Date:   Tue, 22 Mar 2022 13:16:54 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        Gary Guo <gary@...yguo.net>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v5 12/20] vsprintf: add new `%pA` format specifier

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@...yguo.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().