linux-kernel - [PATCH] tty: remove recursive implementation of tty_ldisc

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Message-ID: <20120525111152.7239.99793.stgit@bob.linux.org.uk>
Date:	Fri, 25 May 2012 12:11:54 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	levinsasha928@...il.com, linux-kernel@...r.kernel.org
Subject: [PATCH] tty: remove recursive implementation of tty_ldisc_release

From: Alan Cox <alan@...ux.intel.com>

We need to do this in one pass with the locking requirements we now
have.

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

 drivers/tty/tty_ldisc.c |   40 +++++++++++++++++++++++-----------------
 1 files changed, 23 insertions(+), 17 deletions(-)


diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 833e851..ecfaef5 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -894,6 +894,23 @@ int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
 	tty_ldisc_enable(tty);
 	return 0;
 }
+
+static int tty_ldisc_kill(struct tty_struct *tty)
+{
+	mutex_lock(&tty->ldisc_mutex);
+	/*
+	 * Now kill off the ldisc
+	 */
+	tty_ldisc_close(tty, tty->ldisc);
+	tty_ldisc_put(tty->ldisc);
+	/* Force an oops if we mess this up */
+	tty->ldisc = NULL;
+
+	/* Ensure the next open requests the N_TTY ldisc */
+	tty_set_termios_ldisc(tty, N_TTY);
+	mutex_unlock(&tty->ldisc_mutex);
+}
+
 /**
  *	tty_ldisc_release		-	release line discipline
  *	@tty: tty being shut down
@@ -912,30 +929,19 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
 	 * race with the set_ldisc code path.
 	 */
 
-	/* We don't give a monkeys' about the o_tty lock here but we
-	   must do both to avoid lock inversions against another single
-	   locking case */
 	tty_unlock_pair(tty, o_tty);
 	tty_ldisc_halt(tty);
 	tty_ldisc_flush_works(tty);
+	if (o_tty) {
+		tty_ldisc_halt(o_tty);
+		tty_ldisc_flush_works(o_tty);
+	}
 	tty_lock_pair(tty, o_tty);
 
-	mutex_lock(&tty->ldisc_mutex);
-	/*
-	 * Now kill off the ldisc
-	 */
-	tty_ldisc_close(tty, tty->ldisc);
-	tty_ldisc_put(tty->ldisc);
-	/* Force an oops if we mess this up */
-	tty->ldisc = NULL;
-
-	/* Ensure the next open requests the N_TTY ldisc */
-	tty_set_termios_ldisc(tty, N_TTY);
-	mutex_unlock(&tty->ldisc_mutex);
 
-	/* This will need doing differently if we need to lock */
+	tty_ldisc_kill(tty);
 	if (o_tty)
-		tty_ldisc_release(o_tty, NULL);
+		tty_ldisc_kill(o_tty);
 
 	/* And the memory resources remaining (buffers, termios) will be
 	   disposed of when the kref hits zero */

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