commit 934e6ebf96e8c1a0f299e64129fdaebc1132a427
author Alan Cox <alan@redhat.com> Mon Oct 13 10:40:43 2008 +0100
committer Linus Torvalds <torvalds@linux-foundation.org> Mon Oct 13 09:51:41 2008 -0700
tree ab4bd754997b097f06a5cfefd9e3671d56e628f4
parent 2cb5998b5f0ccc886fdda3509059eef297b49577

tty: Redo current tty locking

Currently it is sometimes locked by the tty mutex and sometimes by the
sighand lock. The latter is in fact correct and now we can hand back referenced
objects we can fix this up without problems around sleeping functions.

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

drivers/char/tty_io.c

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index b5f57d0..f40298e 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -739,13 +739,11 @@
 {
 	struct tty_struct *tty;
 
-	mutex_lock(&tty_mutex);
 	tty = get_current_tty();
 	if (tty) {
 		tty_vhangup(tty);
 		tty_kref_put(tty);
 	}
-	mutex_unlock(&tty_mutex);
 }
 
 /**
@@ -801,11 +799,9 @@
 	struct pid *tty_pgrp = NULL;
 
 
-	mutex_lock(&tty_mutex);
 	tty = get_current_tty();
 	if (tty) {
 		tty_pgrp = get_pid(tty->pgrp);
-		mutex_unlock(&tty_mutex);
 		lock_kernel();
 		if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
 			tty_vhangup(tty);
@@ -822,7 +818,6 @@
 			kill_pgrp(old_pgrp, SIGCONT, on_exit);
 			put_pid(old_pgrp);
 		}
-		mutex_unlock(&tty_mutex);
 		return;
 	}
 	if (tty_pgrp) {
@@ -837,7 +832,6 @@
 	current->signal->tty_old_pgrp = NULL;
 	spin_unlock_irq(&current->sighand->siglock);
 
-	mutex_lock(&tty_mutex);
 	tty = get_current_tty();
 	if (tty) {
 		unsigned long flags;
@@ -854,7 +848,6 @@
 		       " = NULL", tty);
 #endif
 	}
-	mutex_unlock(&tty_mutex);
 
 	/* Now clear signal->tty under the lock */
 	read_lock(&tasklist_lock);
@@ -3180,14 +3173,11 @@
 struct tty_struct *get_current_tty(void)
 {
 	struct tty_struct *tty;
-	WARN_ON_ONCE(!mutex_is_locked(&tty_mutex));
+	unsigned long flags;
+
+	spin_lock_irqsave(&current->sighand->siglock, flags);
 	tty = tty_kref_get(current->signal->tty);
-	/*
-	 * session->tty can be changed/cleared from under us, make sure we
-	 * issue the load. The obtained pointer, when not NULL, is valid as
-	 * long as we hold tty_mutex.
-	 */
-	barrier();
+	spin_unlock_irqrestore(&current->sighand->siglock, flags);
 	return tty;
 }
 EXPORT_SYMBOL_GPL(get_current_tty);