proc: turn signal_struct->count into "int nr_threads"

No functional changes, just s/atomic_t count/int nr_threads/.

With the recent changes this counter has a single user, get_nr_threads()
And, none of its callers need the really accurate number of threads, not
to mention each caller obviously races with fork/exit.  It is only used to
report this value to the user-space, except first_tid() uses it to avoid
the unnecessary while_each_thread() loop in the unlikely case.

It is a bit sad we need a word in struct signal_struct for this, perhaps
we can change get_nr_threads() to approximate the number of threads using
signal->live and kill ->nr_threads later.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 5 insertions, 8 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 357d443d5a00..ceffc67b564a 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -83,14 +83,10 @@ static void __exit_signal(struct task_struct *tsk)
         struct sighand_struct *sighand;
         struct tty_struct *uninitialized_var(tty);
 
-        BUG_ON(!sig);
-        BUG_ON(!atomic_read(&sig->count));
-
         sighand = rcu_dereference_check(tsk->sighand,
                                         rcu_read_lock_held() ||
                                         lockdep_tasklist_lock_is_held());
         spin_lock(&sighand->siglock);
-        atomic_dec(&sig->count);
 
         posix_cpu_timers_exit(tsk);
         if (group_dead) {
@@ -130,6 +126,7 @@ static void __exit_signal(struct task_struct *tsk)
                 sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
         }
 
+        sig->nr_threads--;
         __unhash_process(tsk, group_dead);
 
         /*
diff --git a/kernel/fork.c b/kernel/fork.c
index 40cd099cfc1b..d32410bd4be7 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -877,9 +877,9 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
         if (!sig)
                 return -ENOMEM;
 
-        atomic_set(&sig->sigcnt, 1);
-        atomic_set(&sig->count, 1);
+        sig->nr_threads = 1;
         atomic_set(&sig->live, 1);
+        atomic_set(&sig->sigcnt, 1);
         init_waitqueue_head(&sig->wait_chldexit);
         if (clone_flags & CLONE_NEWPID)
                 sig->flags |= SIGNAL_UNKILLABLE;
@@ -1256,9 +1256,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         }
 
         if (clone_flags & CLONE_THREAD) {
-                atomic_inc(&current->signal->sigcnt);
-                atomic_inc(&current->signal->count);
+                current->signal->nr_threads++;
                 atomic_inc(&current->signal->live);
+                atomic_inc(&current->signal->sigcnt);
                 p->group_leader = current->group_leader;
                 list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
         }