linux-kernel - Re: [PATCH v3] cleanup: adjust scoped_guard() macros to avoid potential warning

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Message-ID: <a7eec76f-1fbc-4fef-9b6d-15b588eacecb@intel.com>
Date: Wed, 23 Oct 2024 15:43:22 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: <linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>,
	<oe-kbuild-all@...ts.linux.dev>, <amadeuszx.slawinski@...ux.intel.com>, "Tony
 Nguyen" <anthony.l.nguyen@...el.com>,
	<nex.sw.ncis.osdt.itp.upstreaming@...el.com>, <netdev@...r.kernel.org>,
	Markus Elfring <Markus.Elfring@....de>, Kees Cook <keescook@...omium.org>,
	David Lechner <dlechner@...libre.com>, Dan Carpenter <error27@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...el.com>, Dmitry Torokhov
	<dmitry.torokhov@...il.com>, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v3] cleanup: adjust scoped_guard() macros to avoid
 potential warning

On 10/18/24 12:50, Peter Zijlstra wrote:
> On Sun, Oct 13, 2024 at 12:01:24PM +0800, kernel test robot wrote:
>>>> drivers/firewire/core-transaction.c:912:2: warning: variable 'handler' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
>>       912 |         scoped_guard(rcu) {
>>           |         ^~~~~~~~~~~~~~~~~
>>     include/linux/cleanup.h:197:2: note: expanded from macro 'scoped_guard'
>>       197 |         __scoped_guard(_name, /* empty */, __UNIQUE_ID(label), args)
>>           |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>     include/linux/cleanup.h:190:3: note: expanded from macro '__scoped_guard'
>>       190 |                 if (!__guard_ptr(_name)(&scope) && __is_cond_ptr(_name)) {      \
>>           |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>     include/linux/compiler.h:55:28: note: expanded from macro 'if'
>>        55 | #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
>>           |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>     include/linux/compiler.h:57:30: note: expanded from macro '__trace_if_var'
>>        57 | #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
>>           |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>     drivers/firewire/core-transaction.c:921:7: note: uninitialized use occurs here
>>       921 |         if (!handler)
>>           |              ^~~~~~~
>>     include/linux/compiler.h:55:47: note: expanded from macro 'if'
>>        55 | #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
>>           |                                               ^~~~
>>     include/linux/compiler.h:57:52: note: expanded from macro '__trace_if_var'
>>        57 | #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
>>           |                                                    ^~~~
>>     drivers/firewire/core-transaction.c:912:2: note: remove the 'if' if its condition is always false
>>       912 |         scoped_guard(rcu) {
>>           |         ^
>>     include/linux/cleanup.h:197:2: note: expanded from macro 'scoped_guard'
>>       197 |         __scoped_guard(_name, /* empty */, __UNIQUE_ID(label), args)
>>           |         ^
>>     include/linux/cleanup.h:190:3: note: expanded from macro '__scoped_guard'
>>       190 |                 if (!__guard_ptr(_name)(&scope) && __is_cond_ptr(_name)) {      \
>>           |                 ^
>>     include/linux/compiler.h:55:23: note: expanded from macro 'if'
>>        55 | #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
>>           |                       ^
>>     drivers/firewire/core-transaction.c:903:36: note: initialize the variable 'handler' to silence this warning
>>       903 |         struct fw_address_handler *handler;
>>           |                                           ^
>>           |                                            = NULL
>>     1 warning generated.
> 
> So this goes away when we do:
> 
> --- a/include/linux/cleanup.h
> +++ b/include/linux/cleanup.h
> @@ -323,7 +323,7 @@ static __maybe_unused const bool class_#
>    */
>   #define __scoped_guard(_name, _fail, _label, args...)				\
>   	for (CLASS(_name, scope)(args);	true; ({ goto _label; }))		\
> -		if (!__guard_ptr(_name)(&scope) && __is_cond_ptr(_name)) {	\
> +		if (__is_cond_ptr(_name) && !__guard_ptr(_name)(&scope)) {	\

but this will purge the attempt to call __guard_ptr(), and thus newer
lock ;) good that there is at least some comment above

FTR, I have resolved this via v4
https://lore.kernel.org/netdev/20241018113823.171256-1-przemyslaw.kitszel@intel.com/T/

>   			_fail;							\
>   _label:										\
>   			break;							\