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

[Peter Zijlstra]

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)) {	\
 			_fail;							\
 _label:										\
 			break;							\