merge task_work and rcu_head, get rid of separate allocation for keyring case

task_work and rcu_head are identical now; merge them (calling the result
struct callback_head, rcu_head #define'd to it), kill separate allocation
in security/keys since we can just use cred->rcu now.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/sched.h

@@ -1405,7 +1405,7 @@ struct task_struct {
 	int (*notifier)(void *priv);
 	void *notifier_data;
 	sigset_t *notifier_mask;
-	void *task_works;
+	struct callback_head *task_works;
 
 	struct audit_context *audit_context;
 #ifdef CONFIG_AUDITSYSCALL

include/linux/task_work.h

@@ -4,22 +4,16 @@
 #include <linux/list.h>
 #include <linux/sched.h>
 
-struct task_work;
-typedef void (*task_work_func_t)(struct task_work *);
-
-struct task_work {
-	struct task_work *next;
-	task_work_func_t func;
-};
+typedef void (*task_work_func_t)(struct callback_head *);
 
 static inline void
-init_task_work(struct task_work *twork, task_work_func_t func)
+init_task_work(struct callback_head *twork, task_work_func_t func)
 {
 	twork->func = func;
 }
 
-int task_work_add(struct task_struct *task, struct task_work *twork, bool);
-struct task_work *task_work_cancel(struct task_struct *, task_work_func_t);
+int task_work_add(struct task_struct *task, struct callback_head *twork, bool);
+struct callback_head *task_work_cancel(struct task_struct *, task_work_func_t);
 void task_work_run(void);
 
 static inline void exit_task_work(struct task_struct *task)

include/linux/types.h

@@ -246,14 +246,15 @@ struct ustat {
 };
 
 /**
- * struct rcu_head - callback structure for use with RCU
+ * struct callback_head - callback structure for use with RCU and task_work
  * @next: next update requests in a list
  * @func: actual update function to call after the grace period.
  */
-struct rcu_head {
-	struct rcu_head *next;
-	void (*func)(struct rcu_head *head);
+struct callback_head {
+	struct callback_head *next;
+	void (*func)(struct callback_head *head);
 };
+#define rcu_head callback_head
 
 #endif	/* __KERNEL__ */
 #endif /*  __ASSEMBLY__ */

kernel/irq/manage.c

@@ -781,7 +781,7 @@ static void wake_threads_waitq(struct irq_desc *desc)
 		wake_up(&desc->wait_for_threads);
 }
 
-static void irq_thread_dtor(struct task_work *unused)
+static void irq_thread_dtor(struct callback_head *unused)
 {
 	struct task_struct *tsk = current;
 	struct irq_desc *desc;
@@ -813,7 +813,7 @@ static void irq_thread_dtor(struct task_work *unused)
  */
 static int irq_thread(void *data)
 {
-	struct task_work on_exit_work;
+	struct callback_head on_exit_work;
 	static const struct sched_param param = {
 		.sched_priority = MAX_USER_RT_PRIO/2,
 	};

kernel/task_work.c

@@ -3,7 +3,7 @@
 #include <linux/tracehook.h>
 
 int
-task_work_add(struct task_struct *task, struct task_work *twork, bool notify)
+task_work_add(struct task_struct *task, struct callback_head *twork, bool notify)
 {
 	unsigned long flags;
 	int err = -ESRCH;
@@ -19,8 +19,8 @@ task_work_add(struct task_struct *task, struct task_work *twork, bool notify)
 	 */
 	raw_spin_lock_irqsave(&task->pi_lock, flags);
 	if (likely(!(task->flags & PF_EXITING))) {
-		struct task_work *last = task->task_works;
-		struct task_work *first = last ? last->next : twork;
+		struct callback_head *last = task->task_works;
+		struct callback_head *first = last ? last->next : twork;
 		twork->next = first;
 		if (last)
 			last->next = twork;
@@ -35,16 +35,16 @@ task_work_add(struct task_struct *task, struct task_work *twork, bool notify)
 	return err;
 }
 
-struct task_work *
+struct callback_head *
 task_work_cancel(struct task_struct *task, task_work_func_t func)
 {
 	unsigned long flags;
-	struct task_work *last, *res = NULL;
+	struct callback_head *last, *res = NULL;
 
 	raw_spin_lock_irqsave(&task->pi_lock, flags);
 	last = task->task_works;
 	if (last) {
-		struct task_work *q = last, *p = q->next;
+		struct callback_head *q = last, *p = q->next;
 		while (1) {
 			if (p->func == func) {
 				q->next = p->next;
@@ -66,7 +66,7 @@ task_work_cancel(struct task_struct *task, task_work_func_t func)
 void task_work_run(void)
 {
 	struct task_struct *task = current;
-	struct task_work *p, *q;
+	struct callback_head *p, *q;
 
 	raw_spin_lock_irq(&task->pi_lock);
 	p = task->task_works;

security/keys/internal.h

@@ -148,12 +148,8 @@ extern key_ref_t lookup_user_key(key_serial_t id, unsigned long flags,
 #define KEY_LOOKUP_PARTIAL	0x02
 #define KEY_LOOKUP_FOR_UNLINK	0x04
 
-struct kludge {	/* this will die off very soon */
-	struct task_work twork;
-	struct cred *cred;
-};
 extern long join_session_keyring(const char *name);
-extern void key_change_session_keyring(struct task_work *twork);
+extern void key_change_session_keyring(struct callback_head *twork);
 
 extern struct work_struct key_gc_work;
 extern unsigned key_gc_delay;

security/keys/keyctl.c

@@ -1456,8 +1456,7 @@ long keyctl_session_to_parent(void)
 {
 	struct task_struct *me, *parent;
 	const struct cred *mycred, *pcred;
-	struct kludge *newwork;
-	struct task_work *oldwork;
+	struct callback_head *newwork, *oldwork;
 	key_ref_t keyring_r;
 	struct cred *cred;
 	int ret;
@@ -1467,20 +1466,17 @@ long keyctl_session_to_parent(void)
 		return PTR_ERR(keyring_r);
 
 	ret = -ENOMEM;
-	newwork = kmalloc(sizeof(struct kludge), GFP_KERNEL);
-	if (!newwork)
-		goto error_keyring;
 
 	/* our parent is going to need a new cred struct, a new tgcred struct
 	 * and new security data, so we allocate them here to prevent ENOMEM in
 	 * our parent */
 	cred = cred_alloc_blank();
 	if (!cred)
-		goto error_newwork;
+		goto error_keyring;
+	newwork = &cred->rcu;
 
 	cred->tgcred->session_keyring = key_ref_to_ptr(keyring_r);
-	init_task_work(&newwork->twork, key_change_session_keyring);
-	newwork->cred = cred;
+	init_task_work(newwork, key_change_session_keyring);
 
 	me = current;
 	rcu_read_lock();
@@ -1529,24 +1525,18 @@ long keyctl_session_to_parent(void)
 
 	/* the replacement session keyring is applied just prior to userspace
 	 * restarting */
-	ret = task_work_add(parent, &newwork->twork, true);
+	ret = task_work_add(parent, newwork, true);
 	if (!ret)
 		newwork = NULL;
 unlock:
 	write_unlock_irq(&tasklist_lock);
 	rcu_read_unlock();
-	if (oldwork) {
-		put_cred(container_of(oldwork, struct kludge, twork)->cred);
-		kfree(oldwork);
-	}
-	if (newwork) {
-		put_cred(newwork->cred);
-		kfree(newwork);
-	}
+	if (oldwork)
+		put_cred(container_of(oldwork, struct cred, rcu));
+	if (newwork)
+		put_cred(cred);
 	return ret;
 
-error_newwork:
-	kfree(newwork);
 error_keyring:
 	key_ref_put(keyring_r);
 	return ret;

security/keys/process_keys.c

@@ -834,13 +834,11 @@ long join_session_keyring(const char *name)
  * Replace a process's session keyring on behalf of one of its children when
  * the target  process is about to resume userspace execution.
  */
-void key_change_session_keyring(struct task_work *twork)
+void key_change_session_keyring(struct callback_head *twork)
 {
 	const struct cred *old = current_cred();
-	struct kludge *p = container_of(twork, struct kludge, twork);
-	struct cred *new = p->cred;
+	struct cred *new = container_of(twork, struct cred, rcu);
 
-	kfree(p);
 	if (unlikely(current->flags & PF_EXITING)) {
 		put_cred(new);
 		return;