[PATCH] do_acct_process(): don't take tty_mutex

No need to take the global tty_mutex, signal->tty->driver can't go away while
we are holding ->siglock.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 5 deletions

diff --git a/kernel/acct.c b/kernel/acct.c
index ca5619039367..69a40c9777a2 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -485,12 +485,9 @@ static void do_acct_process(struct file *file)
         ac.ac_ppid = current->parent->tgid;
 #endif
 
-        mutex_lock(&tty_mutex);
-        tty = get_current_tty();
-        ac.ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
-        mutex_unlock(&tty_mutex);
-
         spin_lock_irq(&current->sighand->siglock);
+        tty = current->signal->tty;
+        ac.ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
         ac.ac_utime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_utime)));
         ac.ac_stime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_stime)));
         ac.ac_flag = pacct->ac_flag;