wait: explain the shadowing and type inconsistencies

Stick in a comment before someone else tries to fix the sparse warning this generates. Suggested-by: Andrew Morton <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> Link: http://lkml.kernel.org/n/[email protected] Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
cbmeeks · Apr 18, 2014 · 8b32201 · 8b32201
1 parent 9cc2368
commit 8b32201
Showing 1 changed file with 13 additions and 1 deletion.
diff --git a/include/linux/wait.h b/include/linux/wait.h
@@ -191,11 +191,23 @@ wait_queue_head_t *bit_waitqueue(void *, int);
 	(!__builtin_constant_p(state) ||				\
 		state == TASK_INTERRUPTIBLE || state == TASK_KILLABLE)	\
 
+/*
+ * The below macro ___wait_event() has an explicit shadow of the __ret
+ * variable when used from the wait_event_*() macros.
+ *
+ * This is so that both can use the ___wait_cond_timeout() construct
+ * to wrap the condition.
+ *
+ * The type inconsistency of the wait_event_*() __ret variable is also
+ * on purpose; we use long where we can return timeout values and int
+ * otherwise.
+ */
+
 #define ___wait_event(wq, condition, state, exclusive, ret, cmd)	\
 ({									\
 	__label__ __out;						\
 	wait_queue_t __wait;						\
-	long __ret = ret;						\
+	long __ret = ret;	/* explicit shadow */			\
 									\
 	INIT_LIST_HEAD(&__wait.task_list);				\
 	if (exclusive)							\