linux-kernel - [PATCH] n_tty: Protect minimum_to_wake reset for concurrent readers

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Date:	Thu,  7 Nov 2013 14:01:57 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH] n_tty: Protect minimum_to_wake reset for concurrent readers

With multiple, concurrent readers (each waiting to acquire the
atomic_read_lock mutex), a departing reader may mistakenly reset
minimum_to_wake after a new reader has already set a new value.

Protect the minimum_to_wake reset with the atomic_read_lock critical
section.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/n_tty.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index ce11cd5..bf9650d 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2253,12 +2253,12 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
 	n_tty_set_room(tty);
 	up_read(&tty->termios_rwsem);
 
-	mutex_unlock(&ldata->atomic_read_lock);
 	remove_wait_queue(&tty->read_wait, &wait);
-
 	if (!waitqueue_active(&tty->read_wait))
 		ldata->minimum_to_wake = minimum;
 
+	mutex_unlock(&ldata->atomic_read_lock);
+
 	__set_current_state(TASK_RUNNING);
 	if (b - buf)
 		retval = b - buf;
-- 
1.8.1.2

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