[PATCH] do_task_stat: don't take tty_mutex

Oleg Nesterov
2006-10-22T15:57:50Z

Depends on
tty-signal-tty-locking.patch

->signal->tty is protected by ->siglock, no need to take the global tty_mutex.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- rc2-mm2/fs/proc/array.c~ 2006-10-22 19:28:17.000000000 +0400
+++ rc2-mm2/fs/proc/array.c 2006-10-22 19:45:52.000000000 +0400
@@ -346,20 +346,13 @@ static int do_task_stat(struct task_stru
sigemptyset(&sigcatch);
cutime = cstime = utime = stime = cputime_zero;

- mutex_lock(&tty_mutex);
rcu_read_lock();
if (lock_task_sighand(task, &flags)) {
struct signal_struct *sig = task->signal;
- struct tty_struct *tty = sig->tty;

- if (tty) {
- /*
- * sig->tty is not stable, but tty_mutex
- * protects us from release_dev(tty)
- */
- barrier();
- tty_pgrp = tty->pgrp;
- tty_nr = new_encode_dev(tty_devnum(tty));
+ if (sig->tty) {
+ tty_pgrp = sig->tty->pgrp;
+ tty_nr = new_encode_dev(tty_devnum(sig->tty));
}

num_threads = atomic_read(&sig->count);
@@ -395,7 +388,6 @@ static int do_task_stat(struct task_stru
unlock_task_sighand(task, &flags);
}
rcu_read_unlock();
- mutex_unlock(&tty_mutex);

if (!whole || num_threads<2)
wchan = get_wchan(task);