linux-kernel - [PATCH 1/8] tty: Fix race in the flush for some ldiscs

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Date:	Thu, 15 Jan 2009 13:30:25 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/8] tty: Fix race in the flush for some ldiscs

From: Alan Cox <alan@...hat.com>

If you issue an ioctl to flush a tty as the line discipline is changing or
otherwise unplugged you can get a crash. The bug is very old but the rest
of the BKL lock dropping and some very "good" luck on Ingo's part caught
an example.

Use the correct ldisc_ref form so that we wait for the ldisc change to
complete and then flush

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

 drivers/char/tty_ioctl.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)


diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index a408c8e..6f4c7d0 100644
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -1057,7 +1057,7 @@ int tty_perform_flush(struct tty_struct *tty, unsigned long arg)
 	if (retval)
 		return retval;
 
-	ld = tty_ldisc_ref(tty);
+	ld = tty_ldisc_ref_wait(tty);
 	switch (arg) {
 	case TCIFLUSH:
 		if (ld && ld->ops->flush_buffer)

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