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

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

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

1 files changed, 4 insertions, 12 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 25e917fb4739..b0cd014a39bd 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -346,20 +346,13 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
         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_struct *task, char * buffer, int whole)
                 unlock_task_sighand(task, &flags);
         }
         rcu_read_unlock();
-        mutex_unlock(&tty_mutex);
 
         if (!whole || num_threads<2)
                 wchan = get_wchan(task);