linux-kernel - [PATCH -next 12/27] tty: Document check_tty_count() requires tty

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Message-Id: <1413491125-20134-13-git-send-email-peter@hurleysoftware.com>
Date:	Thu, 16 Oct 2014 16:25:10 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>,
	linux-serial@...r.kernel.org,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH -next 12/27] tty: Document check_tty_count() requires tty_lock held

Holding the tty_lock() is necessary to prevent concurrent changes
to the tty count that may cause it to differ from the open file
list count. The tty_lock() is already held at all call sites.

NB: Note that the check for the pty master tty count is safe because
the slave's tty_lock() is held while decrementing the pty master
tty count.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/tty_io.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 50118ce..5c09cc4 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -275,6 +275,7 @@ int tty_paranoia_check(struct tty_struct *tty, struct inode *inode,
 	return 0;
 }
 
+/* Caller must hold tty_lock */
 static int check_tty_count(struct tty_struct *tty, const char *routine)
 {
 #ifdef CHECK_TTY_COUNT
-- 
2.1.1

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