[PATCH] sched/wake_q: Restore task_struct::wake_q type safety

[Ingo Molnar]

Linus correctly observed that task_struct::wake_q is an opaque pointer
in a rather ugly way, through which we lose not just readability but
also type safety, for only marginal savings in sched.h.

Just restore the 'struct wake_q_node' type in sched.h and include
sched.h in sched/wake_q.h.

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 include/linux/sched.h        | 6 +++++-
 include/linux/sched/wake_q.h | 6 +-----
 ipc/msg.c                    | 1 -
 kernel/fork.c                | 2 +-
 kernel/sched/core.c          | 6 +++---
 5 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2cc4d7902418..d67eee84fd43 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -476,6 +476,10 @@ enum perf_event_task_context {
 	perf_nr_task_contexts,
 };
 
+struct wake_q_node {
+	struct wake_q_node *next;
+};
+
 struct task_struct {
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 	/*
@@ -765,7 +769,7 @@ struct task_struct {
 	/* Protection of the PI data structures: */
 	raw_spinlock_t			pi_lock;
 
-	void				*wake_q;
+	struct wake_q_node		wake_q;
 
 #ifdef CONFIG_RT_MUTEXES
 	/* PI waiters blocked on a rt_mutex held by this task: */
diff --git a/include/linux/sched/wake_q.h b/include/linux/sched/wake_q.h
index e6774a0385fb..d03d8a9047dc 100644
--- a/include/linux/sched/wake_q.h
+++ b/include/linux/sched/wake_q.h
@@ -28,11 +28,7 @@
  * wakeup condition has in fact occurred.
  */
 
-struct task_struct;
-
-struct wake_q_node {
-	struct wake_q_node *next;
-};
+#include <linux/sched.h>
 
 struct wake_q_head {
 	struct wake_q_node *first;
diff --git a/ipc/msg.c b/ipc/msg.c
index ecc387e573f6..104926dc72be 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -30,7 +30,6 @@
 #include <linux/proc_fs.h>
 #include <linux/list.h>
 #include <linux/security.h>
-#include <linux/sched.h>
 #include <linux/sched/wake_q.h>
 #include <linux/syscalls.h>
 #include <linux/audit.h>
diff --git a/kernel/fork.c b/kernel/fork.c
index 4a033bb7d660..68b1706c75d0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -548,7 +548,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 #endif
 	tsk->splice_pipe = NULL;
 	tsk->task_frag.page = NULL;
-	tsk->wake_q = NULL;
+	tsk->wake_q.next = NULL;
 
 	account_kernel_stack(tsk, 1);
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0abcf7307428..a4fdb6b03577 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -431,7 +431,7 @@ static bool set_nr_if_polling(struct task_struct *p)
 
 void wake_q_add(struct wake_q_head *head, struct task_struct *task)
 {
-	struct wake_q_node *node = (void *)&task->wake_q;
+	struct wake_q_node *node = &task->wake_q;
 
 	/*
 	 * Atomically grab the task, if ->wake_q is !nil already it means
@@ -460,11 +460,11 @@ void wake_up_q(struct wake_q_head *head)
 	while (node != WAKE_Q_TAIL) {
 		struct task_struct *task;
 
-		task = container_of((void *)node, struct task_struct, wake_q);
+		task = container_of(node, struct task_struct, wake_q);
 		BUG_ON(!task);
 		/* Task can safely be re-inserted now: */
 		node = node->next;
-		task->wake_q = NULL;
+		task->wake_q.next = NULL;
 
 		/*
 		 * wake_up_process() implies a wmb() to pair with the queueing