From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759299Ab1KWAve (ORCPT ); Tue, 22 Nov 2011 19:51:34 -0500 Received: from cantor2.suse.de ([195.135.220.15]:42842 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759098Ab1KWAkz (ORCPT ); Tue, 22 Nov 2011 19:40:55 -0500 X-Mailbox-Line: From gregkh@clark.kroah.org Tue Nov 22 16:24:06 2011 Message-Id: <20111123002406.590288296@clark.kroah.org> User-Agent: quilt/0.48-20.1.2 Date: Tue, 22 Nov 2011 16:23:28 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Stephen Boyd Subject: [21/53] tty: hvc_dcc: Fix duplicate character inputs In-Reply-To: <20111123002419.GA8531@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Stephen Boyd commit c2a3e84f950e7ddba1f3914b005861d46ae60359 upstream. Reading from the DCC grabs a character from the buffer and clears the status bit. Since this is a context-changing operation, instructions following the character read that rely on the status bit being accurate need to be synchronized with an ISB. In this case, the status bit check needs to execute after the character read otherwise we run the risk of reading the character and checking the status bit before the read can clear the status bit in the first place. When this happens, the user will see the same character they typed twice, instead of once. Add an ISB after the read and the write, so that the status check is synchronized with the read/write operations. Signed-off-by: Stephen Boyd Signed-off-by: Greg Kroah-Hartman --- drivers/tty/hvc/hvc_dcc.c | 2 ++ 1 file changed, 2 insertions(+) --- a/drivers/tty/hvc/hvc_dcc.c +++ b/drivers/tty/hvc/hvc_dcc.c @@ -46,6 +46,7 @@ static inline char __dcc_getchar(void) asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" : "=r" (__c)); + isb(); return __c; } @@ -55,6 +56,7 @@ static inline void __dcc_putchar(char c) asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char" : /* no output register */ : "r" (c)); + isb(); } static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)