tty: simplify calling of put_pid.

This patch should contain no functional changes.

At some point I got confused and thought put_pid could not be called while a
spin lock was held.  While it may be nice to avoid that to reduce lock hold
times put_pid can be safely called while we hold a spin lock.

This patch removes all of the complications from the code introduced by my
misunderstanding, making the code a little more readable.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/tty_io.c

@@ -153,8 +153,7 @@ int tty_ioctl(struct inode * inode, struct file * file,
 	      unsigned int cmd, unsigned long arg);
 static int tty_fasync(int fd, struct file * filp, int on);
 static void release_tty(struct tty_struct *tty, int idx);
-static struct pid *__proc_set_tty(struct task_struct *tsk,
-				struct tty_struct *tty);
+static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);
 
 /**
  *	alloc_tty_struct	-	allocate a tty object
@@ -1532,10 +1531,9 @@ void disassociate_ctty(int on_exit)
 	}
 
 	spin_lock_irq(&current->sighand->siglock);
-	tty_pgrp = current->signal->tty_old_pgrp;
+	put_pid(current->signal->tty_old_pgrp);
 	current->signal->tty_old_pgrp = NULL;
 	spin_unlock_irq(&current->sighand->siglock);
-	put_pid(tty_pgrp);
 
 	mutex_lock(&tty_mutex);
 	/* It is possible that do_tty_hangup has free'd this tty */
@@ -2506,7 +2504,6 @@ static int tty_open(struct inode * inode, struct file * filp)
 	int index;
 	dev_t device = inode->i_rdev;
 	unsigned short saved_flags = filp->f_flags;
-	struct pid *old_pgrp;
 
 	nonseekable_open(inode, filp);
 	
@@ -2600,17 +2597,15 @@ got_driver:
 		goto retry_open;
 	}
 
-	old_pgrp = NULL;
 	mutex_lock(&tty_mutex);
 	spin_lock_irq(&current->sighand->siglock);
 	if (!noctty &&
 	    current->signal->leader &&
 	    !current->signal->tty &&
 	    tty->session == NULL)
-		old_pgrp = __proc_set_tty(current, tty);
+		__proc_set_tty(current, tty);
 	spin_unlock_irq(&current->sighand->siglock);
 	mutex_unlock(&tty_mutex);
-	put_pid(old_pgrp);
 	return 0;
 }
 
@@ -3835,9 +3830,8 @@ void proc_clear_tty(struct task_struct *p)
 	spin_unlock_irq(&p->sighand->siglock);
 }
 
-static struct pid *__proc_set_tty(struct task_struct *tsk, struct tty_struct *tty)
+static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty)
 {
-	struct pid *old_pgrp;
 	if (tty) {
 		/* We should not have a session or pgrp to here but.... */
 		put_pid(tty->session);
@@ -3845,21 +3839,16 @@ static struct pid *__proc_set_tty(struct task_struct *tsk, struct tty_struct *tt
 		tty->session = get_pid(task_session(tsk));
 		tty->pgrp = get_pid(task_pgrp(tsk));
 	}
-	old_pgrp = tsk->signal->tty_old_pgrp;
+	put_pid(tsk->signal->tty_old_pgrp);
 	tsk->signal->tty = tty;
 	tsk->signal->tty_old_pgrp = NULL;
-	return old_pgrp;
 }
 
 void proc_set_tty(struct task_struct *tsk, struct tty_struct *tty)
 {
-	struct pid *old_pgrp;
-
 	spin_lock_irq(&tsk->sighand->siglock);
-	old_pgrp = __proc_set_tty(tsk, tty);
+	__proc_set_tty(tsk, tty);
 	spin_unlock_irq(&tsk->sighand->siglock);
-
-	put_pid(old_pgrp);
 }
 
 struct tty_struct *get_current_tty(void)