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 <akpm@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-o2ro6f3vkxklni0bc8f7m68s@git.kernel.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 1 deletions

diff --git a/include/linux/wait.h b/include/linux/wait.h
index e7d9d9ed14f5..bd68819f0815 100644
--- 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)                                                  \