From: Peter Hurley <peter@hurleysoftware.com>
Date: Wed, 5 Nov 2014 17:12:55 +0000 (-0500)
Subject: tty: Document check_tty_count() requires tty_lock held
X-Git-Tag: firefly_0821_release~176^2~2678^2~182
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;ds=sidebyside;h=deb287e7401bbbf7803731805acbda1d983d1999;p=firefly-linux-kernel-4.4.55.git

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.

Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index b008e2b38d54..adbd9acf817f 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