linux-kernel - [PATCH 2/5] tty: Push the lock down further into the ldisc code

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Message-ID: <20091118142548.3806.34931.stgit@localhost.localdomain>
Date:	Wed, 18 Nov 2009 14:26:03 +0000
From:	Alan Cox <alan@...ux.intel.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] tty: Push the lock down further into the ldisc code

Signed-off-by: Alan Cox <alan@...ux.intel.com>
---

 drivers/char/tty_io.c    |    2 --
 drivers/char/tty_ldisc.c |   12 +++++++++---
 2 files changed, 9 insertions(+), 5 deletions(-)


diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 05e94a2..a1b1ff6 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1347,9 +1347,7 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
 	 * If we fail here just call release_tty to clean up.  No need
 	 * to decrement the use counts, as release_tty doesn't care.
 	 */
-	lock_kernel();
 	retval = tty_ldisc_setup(tty, tty->link);
-	unlock_kernel();
 	if (retval)
 		goto release_mem_out;
 	return tty;
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index d914e77..3f653f7 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -445,8 +445,14 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 {
 	WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
-	if (ld->ops->open)
-		return ld->ops->open(tty);
+	if (ld->ops->open) {
+		int ret;
+                /* BKL here locks versus a hangup event */
+		lock_kernel();
+		ret = ld->ops->open(tty);
+		unlock_kernel();
+		return ret;
+	}
 	return 0;
 }
 
@@ -566,6 +572,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 		return 0;
 	}
 
+	unlock_kernel();
 	/*
 	 *	Problem: What do we do if this blocks ?
 	 *	We could deadlock here
@@ -573,7 +580,6 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
 	tty_wait_until_sent(tty, 0);
 
-	unlock_kernel();
 	mutex_lock(&tty->ldisc_mutex);
 
 	/*

--
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