From c0fdfb80382e4901473ce0e31d1e7833c1d297be Mon Sep 17 00:00:00 2001 From: Peter Hurley <peter@hurleysoftware.com> Date: Sun, 9 Feb 2014 20:59:04 -0500 Subject: [PATCH] tty: Fix ref counting for port krefs The tty core supports two models for handling tty_port lifetimes; the tty_port can use the kref supplied by tty_port (which will automatically destruct the tty_port when the ref count drops to zero) or it can destruct the tty_port manually. For tty drivers that choose to use the port kref to manage the tty_port lifetime, it is not possible to safely acquire a port reference conditionally. If the last reference is released after evaluating the condition but before acquiring the reference, a bogus reference will be held while the tty_port destruction commences. Rather, only acquire a port reference if the ref count is non-zero and allow the caller to distinguish if a reference has successfully been acquired. Cc: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Tested-By: Alexander Holler <holler@ahsoftware.de> Signed-off-by: Marcel Holtmann <marcel@holtmann.org> --- include/linux/tty.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/tty.h b/include/linux/tty.h index 90b4fdc8a61f..4781d7b27dd3 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -518,9 +518,9 @@ extern void tty_port_put(struct tty_port *port); static inline struct tty_port *tty_port_get(struct tty_port *port) { - if (port) - kref_get(&port->kref); - return port; + if (port && kref_get_unless_zero(&port->kref)) + return port; + return NULL; } /* If the cts flow control is enabled, return true. */