[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 <oleg@tv-sign.ru>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Jay Lan <jlan@engr.sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 25 insertions, 2 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index f37980df1d58..658838148647 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -847,7 +847,6 @@ static inline int copy_signal(unsigned long clone_flags, struct task_struct * ts
         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);
diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 2654886fe058..7d793d6b1e90 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -412,6 +412,30 @@ err:
         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)
 {
@@ -433,7 +457,7 @@ 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;