tty: Add a kref count

Introduce a kref to the tty structure and use it to protect the tty->signal
tty references. For now we don't introduce it for anything else.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 5 insertions, 4 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 7ce2ebe84796..30de644a40c4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -802,6 +802,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 
         sig->leader = 0;        /* session leadership doesn't inherit */
         sig->tty_old_pgrp = NULL;
+        sig->tty = NULL;
 
         sig->utime = sig->stime = sig->cutime = sig->cstime = cputime_zero;
         sig->gtime = cputime_zero;
@@ -838,6 +839,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 void __cleanup_signal(struct signal_struct *sig)
 {
         exit_thread_group_keys(sig);
+        tty_kref_put(sig->tty);
         kmem_cache_free(signal_cachep, sig);
 }
 
@@ -1227,7 +1229,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
                                 p->nsproxy->pid_ns->child_reaper = p;
 
                         p->signal->leader_pid = pid;
-                        p->signal->tty = current->signal->tty;
+                        tty_kref_put(p->signal->tty);
+                        p->signal->tty = tty_kref_get(current->signal->tty);
                         set_task_pgrp(p, task_pgrp_nr(current));
                         set_task_session(p, task_session_nr(current));
                         attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
diff --git a/kernel/sys.c b/kernel/sys.c
index 038a7bc0901d..234d9454294e 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1060,9 +1060,7 @@ asmlinkage long sys_setsid(void)
         group_leader->signal->leader = 1;
         __set_special_pids(sid);
 
-        spin_lock(&group_leader->sighand->siglock);
-        group_leader->signal->tty = NULL;
-        spin_unlock(&group_leader->sighand->siglock);
+        proc_clear_tty(group_leader);
 
         err = session;
 out: