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 <dlechner@baylibre.com>
Co-developed-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lkml.kernel.org/r/20241001-cleanup-if_not_cond_guard-v1-1-7753810b0f7a@baylibre.com

diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index 0cc66f8d28e7b67231133a4efec6923610cdcd25..e859f79b9d2d9311376ec1c2ea0764bc22b969b7 100644 (file)
--- a/include/linux/cleanup.h
+++ b/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