Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755684AbaLHWWb (ORCPT ); Mon, 8 Dec 2014 17:22:31 -0500 Received: from mail-pd0-f180.google.com ([209.85.192.180]:46077 "EHLO mail-pd0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755591AbaLHWWY (ORCPT ); Mon, 8 Dec 2014 17:22:24 -0500 Date: Mon, 8 Dec 2014 14:22:20 -0800 From: Jeremiah Mahler To: Denis Du Cc: "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] TTY: missing a lock to access the ldisk buffer Message-ID: <20141208222220.GA9912@hudson.localdomain> Mail-Followup-To: Jeremiah Mahler , Denis Du , "linux-kernel@vger.kernel.org" References: <694700710.6880446.1418070480521.JavaMail.yahoo@jws10627.mail.bf1.yahoo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <694700710.6880446.1418070480521.JavaMail.yahoo@jws10627.mail.bf1.yahoo.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Denis, This patch won't apply to linux-next 20141208 so I can't test it :-( Which kernel does this patch apply to? On Mon, Dec 08, 2014 at 08:28:00PM +0000, Denis Du wrote: > Hi, Guys: > I found that the 3.12 kernel tty layer will lose or corrupt data when having a full-duplex communication, especcially in high baudrate, for example 230k for my OMAP5 uart. Eventually I found there is a lock missing between copy data to ldisc layer buffer and copy data from the same buffer to user space. I believe this issue have been existing since 3.8 kernel(since this kernel , it start to remove most of the spin-locks) and I didn't find any fix even through 3.17 kernel. This patch was tested to be works great with no any data loss again. > > > I did try to use the existed lock atomic_read_lock, but it doesn’t work. > > > > Signed-off-by: Hui Du > > > --- > > --- drivers/tty/n_tty.c 2014-10-16 16:39:35.909350338 -0400 > +++ drivers/tty/n_tty.c 2014-10-16 16:49:00.004930469 -0400 > @@ -124,6 +124,7 @@ > > struct mutex atomic_read_lock; > struct mutex output_lock; > + struct mutex read_buf_lock; > }; > > static inline size_t read_cnt(struct n_tty_data *ldata) > @@ -1686,9 +1687,11 @@ > char *fp, int count) > { > int room, n; > + struct n_tty_data *ldata = tty->disc_data; > > down_read(&tty->termios_rwsem); > > + mutex_lock(&ldata->read_buf_lock); > while (1) { > room = receive_room(tty); > n = min(count, room); > @@ -1703,6 +1706,7 @@ > > tty->receive_room = room; > n_tty_check_throttle(tty); > + mutex_unlock(&ldata->read_buf_lock); > up_read(&tty->termios_rwsem); > } > > @@ -1713,7 +1717,7 @@ > int room, n, rcvd = 0; > > down_read(&tty->termios_rwsem); > - > + mutex_lock(&ldata->read_buf_lock); > while (1) { > room = receive_room(tty); > n = min(count, room); > @@ -1732,6 +1736,7 @@ > > tty->receive_room = room; > n_tty_check_throttle(tty); > + mutex_unlock(&ldata->read_buf_lock); > up_read(&tty->termios_rwsem); > > return rcvd; > @@ -1880,6 +1885,7 @@ > ldata->overrun_time = jiffies; > mutex_init(&ldata->atomic_read_lock); > mutex_init(&ldata->output_lock); > + mutex_init(&ldata->read_buf_lock); > > tty->disc_data = ldata; > reset_buffer_flags(tty->disc_data); > @@ -1945,6 +1951,8 @@ > size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1); > > retval = 0; > + > + mutex_lock(&ldata->read_buf_lock); > n = min(read_cnt(ldata), N_TTY_BUF_SIZE - tail); > n = min(*nr, n); > if (n) { > @@ -1960,6 +1968,7 @@ > *b += n; > *nr -= n; > } > + mutex_unlock(&ldata->read_buf_lock); > return retval; > } > > @@ -1990,6 +1999,8 @@ > size_t tail; > int ret, found = 0; > bool eof_push = 0; > + > + mutex_lock(&ldata->read_buf_lock); > > /* N.B. avoid overrun if nr == 0 */ > n = min(*nr, read_cnt(ldata)); > @@ -2049,6 +2060,8 @@ > ldata->line_start = ldata->read_tail; > tty_audit_push(tty); > } > + > + mutex_unlock(&ldata->read_buf_lock); > return eof_push ? -EAGAIN : 0; > } > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- - Jeremiah Mahler -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/