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>

1 files changed, 1 insertions, 4 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);
 
         /*