cleanup: Add conditional guard helper

Add a new if_not_guard() macro to cleanup.h for handling
conditional guards such as mutext_trylock().

This is more ergonomic than scoped_guard() for most use cases.
Instead of hiding the error handling statement in the macro args, it
works like a normal if statement and allow the error path to be indented
while the normal code flow path is not indented. And it avoid unwanted
side-effect from hidden for loop in scoped_guard().

Signed-off-by: David Lechner <[email protected]>
Co-developed-by: Fabio M. De Francesco <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Link: https://lkml.kernel.org/r/20241001-cleanup-if_not_cond_guard-v1-1-7753810b0f7a@baylibre.com

Author: dlech

include/linux/cleanup.h

@@ -273,6 +273,12 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
  *	an anonymous instance of the (guard) class, not recommended for
  *	conditional locks.
  *
+ * if_not_guard(name, args...) { <error handling> }:
+ *	convenience macro for conditional guards that calls the statement that
+ *	follows only if the lock was not acquired (typically an error return).
+ *
+ *	Only for conditional locks.
+ *
  * scoped_guard (name, args...) { }:
  *	similar to CLASS(name, scope)(args), except the variable (with the
  *	explicit name 'scope') is declard in a for-loop such that its scope is
@@ -343,6 +349,15 @@ _label:									\
 
 #define scoped_cond_guard(_name, _fail, args...)	\
 	__scoped_cond_guard(_name, _fail, __UNIQUE_ID(label), args)
+
+#define __if_not_guard(_name, _id, args...)		\
+	BUILD_BUG_ON(!__is_cond_ptr(_name));		\
+	CLASS(_name, _id)(args);			\
+	if (!__guard_ptr(_name)(&_id))
+
+#define if_not_guard(_name, args...) \
+	__if_not_guard(_name, __UNIQUE_ID(guard), args)
+
 /*
  * Additional helper macros for generating lock guards with types, either for
  * locks that don't have a native type (eg. RCU, preempt) or those that need a