[PATCH] taskstats: cleanup ->signal->stats allocation

Allocate ->signal->stats on demand in taskstats_exit(), this allows us to
remove taskstats_tgid_alloc() (the last non-trivial inline) from taskstat's
public interface.

Signed-off-by: Oleg Nesterov <[e-mail]>
Cc: Balbir Singh <[e-mail]>
Cc: Shailabh Nagar <[e-mail]>
Cc: Jay Lan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/taskstats_kern.h

···
 	sig->stats = NULL;
 }
 
-static inline void taskstats_tgid_alloc(struct task_struct *tsk)
-{
-	struct signal_struct *sig = tsk->signal;
-	struct taskstats *stats;
-
-	if (sig->stats != NULL)
-		return;
-
-	/* No problem if kmem_cache_zalloc() fails */
-	stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
-
-	spin_lock_irq(&tsk->sighand->siglock);
-	if (!sig->stats) {
-		sig->stats = stats;
-		stats = NULL;
-	}
-	spin_unlock_irq(&tsk->sighand->siglock);
-
-	if (stats)
-		kmem_cache_free(taskstats_cache, stats);
-}
-
 static inline void taskstats_tgid_free(struct signal_struct *sig)
 {
 	if (sig->stats)
···
 static inline void taskstats_exit(struct task_struct *tsk, int group_dead)
 {}
 static inline void taskstats_tgid_init(struct signal_struct *sig)
-{}
-static inline void taskstats_tgid_alloc(struct task_struct *tsk)
 {}
 static inline void taskstats_tgid_free(struct signal_struct *sig)
 {}

kernel/fork.c

···
 	if (clone_flags & CLONE_THREAD) {
 		atomic_inc(&current->signal->count);
 		atomic_inc(&current->signal->live);
-		taskstats_tgid_alloc(current);
 		return 0;
 	}
 	sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);

kernel/taskstats.c

···
 	return rc;
 }
 
+static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
+{
+	struct signal_struct *sig = tsk->signal;
+	struct taskstats *stats;
+
+	if (sig->stats || thread_group_empty(tsk))
+		goto ret;
+
+	/* No problem if kmem_cache_zalloc() fails */
+	stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
+
+	spin_lock_irq(&tsk->sighand->siglock);
+	if (!sig->stats) {
+		sig->stats = stats;
+		stats = NULL;
+	}
+	spin_unlock_irq(&tsk->sighand->siglock);
+
+	if (stats)
+		kmem_cache_free(taskstats_cache, stats);
+ret:
+	return sig->stats;
+}
+
 /* Send pid data out on exit */
 void taskstats_exit(struct task_struct *tsk, int group_dead)
 {
···
 	size = nla_total_size(sizeof(u32)) +
 		nla_total_size(sizeof(struct taskstats)) + nla_total_size(0);
 
-	is_thread_group = (tsk->signal->stats != NULL);
+	is_thread_group = !!taskstats_tgid_alloc(tsk);
 	if (is_thread_group) {
 		/* PID + STATS + TGID + STATS */
 		size = 2 * size;