From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: [PATCH v2 08/14] tty: Convert tty_struct bitfield to ints Date: Wed, 10 Sep 2014 15:06:30 -0400 Message-ID: <1410375996-4693-9-git-send-email-peter@hurleysoftware.com> References: <1409693975-1028-1-git-send-email-peter@hurleysoftware.com> <1410375996-4693-1-git-send-email-peter@hurleysoftware.com> Return-path: In-Reply-To: <1410375996-4693-1-git-send-email-peter@hurleysoftware.com> Sender: linux-kernel-owner@vger.kernel.org To: Greg Kroah-Hartman Cc: Jiri Slaby , One Thousand Gnomes , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Peter Hurley List-Id: linux-serial@vger.kernel.org The stopped, hw_stopped, flow_stopped and packet bits are smp-unsafe and interrupt-unsafe. For example, CPU 0 | CPU 1 | tty->flow_stopped = 1 | tty->hw_stopped = 0 One of these updates will be corrupted, as the bitwise operation on the bitfield is non-atomic. Ensure each flag has a separate memory location, so concurrent updates do not corrupt orthogonal states. Because DEC Alpha EV4 and EV5 cpus (from 1995) perform RMW on smaller-than-machine-word storage, "separate memory location" must be int instead of byte. Signed-off-by: Peter Hurley --- include/linux/tty.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/tty.h b/include/linux/tty.h index 1c3316a..a707196 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -261,7 +261,10 @@ struct tty_struct { unsigned long flags; int count; struct winsize winsize; /* winsize_mutex */ - unsigned char stopped:1, hw_stopped:1, flow_stopped:1, packet:1; + int stopped; + int flow_stopped; + int hw_stopped; + int packet; unsigned char ctrl_status; /* ctrl_lock */ unsigned int receive_room; /* Bytes free for queue */ int flow_change; -- 2.1.0