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tty: remove recursive implementation of tty_ldisc_release

PATCH In review Alan Cox 3 participants 4 messages May 25, 2012 – May 26, 2012 TTY layer and serial drivers

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Alan Cox

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#0 lore raw

PATCH 1/1 tty: remove recursive implementation of tty_ldisc_release

From: Alan Cox <[email protected]>

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

Signed-off-by Alan Cox <[email protected]>

---

 drivers/tty/tty_ldisc.c |   40 +++++++++++++++++++++++-----------------
 1 files changed, 23 insertions(+), 17 deletions(-)
drivers/tty/tty_ldisc.c +23 -17
index 833e851..ecfaef5 100644
@@ -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 */
author
#2 lore raw
Quoted 11 lines · On Fri, 25 May 2012 13:13:15 +0200 Sasha Levin <[email protected]> wrote:
Quoted 7 lines · Alan Cox

From: Alan Cox <[email protected]>

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

Signed-off-by Alan Cox <[email protected]>

---

I don't see any lockdep warnings anymore with this patch applied on top of all others.

Yay thanks for reporting/testing

#3 lore raw
In reply to Alan Cox
Quoted 17 lines · Alan Cox

From: Alan Cox <[email protected]>

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

Signed-off-by Alan Cox <[email protected]>

---

 drivers/tty/tty_ldisc.c |   40 +++++++++++++++++++++++-----------------

 1 files changed, 23 insertions(+), 17 deletions(-)
drivers/tty/tty_ldisc.c +0 -0
index 833e851..ecfaef5 100644

drivers/tty/tty_ldisc.c int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty) · line 898

Quoted 5 lines
drivers/tty/tty_ldisc.c +2 -0
@@ -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)

Maybe the return type should be defined as void to avoid compile warning.

After applying Alan's three patches for addressing tty locks and the patch int the below link:

     http://marc.info/?l=linux-kernel&m=133775308420817&w=2

Looks no lockdep warnings are triggered any more when running 'exit' in shell of ssh session.

So I will send out the formal patch in the above link.

Thanks,

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Ming Lei