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>

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 @@ error:
  * 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;