Re: [PATCH v5 1/5] bug/kunit: Core support for suppressing warning backtraces

[Peter Zijlstra <peterz@infradead.org>]

On Thu, May 29, 2025 at 10:46:15AM -0700, Kees Cook wrote:

> Doing it on the other end doesn't look great (see the other reply).  I was
> suggesting it's not on fast path because the added code is a dependant
> conditional following an "unlikley" conditional. But if you wanted to
> push it totally out of line, we'd likely need to pass __func__ into
> warn_slowpath_fmt() and __warn_printk(), and then have __warn_printk()

warn_slowpath_fmt() already uses buildin_return_address(0), and then it
can use kallsyms to find the symbol name. No need to pass __func__ as a
string.

> return bool to make the call to __WARN_FLAGS() conditional. e.g.:
> 
> -		warn_slowpath_fmt(__FILE__, __LINE__, taint, arg); \
> +		warn_slowpath_fmt(__FILE__, __LINE__, __func__, taint, arg); \
> 
> and:
> 
> -		__warn_printk(arg);					\
> -		__WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
> +		if (__warn_printk(__func__, arg))			\
> +			__WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
> 
> But it still leaves bare __WARN unhandled...

Nah, don't propagate, just eat the __WARN and handle things in
__report_bug(), which is where they all end up.

But the real purpose here seems to be to supress printk output, so why
not use 'suppress_printk' ?