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From: Oleg Nesterov on 18 Mar 2010 18:40
tty_kref_put() have two callsites in copy_process() pathes,

1. if copy_process() suceeds it is called before we copy
signal->tty from parent

2. otherwise it is called from __cleanup_signal() under
bad_fork_cleanup_signal: label

In both cases tty_kref_put() is not right and unneeded because we don't
have the balancing tty_kref_get(). Fortunately, this is harmless because
this can only happen without CLONE_THREAD, and in this case signal->tty
must be NULL.

Remove tty_kref_put() from copy_process() and __cleanup_signal(), and
change another caller of __cleanup_signal(), __exit_signal(), to call
tty_kref_put() by hand.

I hope this change makes sense by itself, but it is also needed to
make ->signal refcountable.

Signed-off-by: Oleg Nesterov <oleg(a)redhat.com>
---

kernel/fork.c | 2 --
kernel/exit.c | 1 +
2 files changed, 1 insertion(+), 2 deletions(-)

--- 34-rc1/kernel/fork.c~7_TTY_PUT 2010-03-17 16:04:22.000000000 +0100
+++ 34-rc1/kernel/fork.c 2010-03-18 22:45:14.000000000 +0100
@@ -896,7 +896,6 @@ static int copy_signal(unsigned long clo
void __cleanup_signal(struct signal_struct *sig)
{
thread_group_cputime_free(sig);
- tty_kref_put(sig->tty);
kmem_cache_free(signal_cachep, sig);
}

@@ -1264,7 +1263,6 @@ static struct task_struct *copy_process(
p->nsproxy->pid_ns->child_reaper = p;

p->signal->leader_pid = pid;
- tty_kref_put(p->signal->tty);
p->signal->tty = tty_kref_get(current->signal->tty);
attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
attach_pid(p, PIDTYPE_SID, task_session(current));
--- 34-rc1/kernel/exit.c~7_TTY_PUT 2010-03-17 20:05:38.000000000 +0100
+++ 34-rc1/kernel/exit.c 2010-03-18 22:46:41.000000000 +0100
@@ -150,6 +150,7 @@ static void __exit_signal(struct task_st
* see account_group_exec_runtime().
*/
task_rq_unlock_wait(tsk);
+ tty_kref_put(sig->tty);
__cleanup_signal(sig);
}
}

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