sched/wait: Explain the shadowing and type inconsistencies

Stick in a comment before someone else tries to fix the sparse warning
this generates.

Requested-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
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 559044c79232dcd27b18a3203d82295866fe949f..2b563a15a77db144f17064c3d138ebf609104f03 100644 (file)
--- 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)                                                  \