From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755331AbaCaAcM (ORCPT ); Sun, 30 Mar 2014 20:32:12 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:36231 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752825AbaC3XY7 (ORCPT ); Sun, 30 Mar 2014 19:24:59 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Patrick Boettcher" , "Mauro Carvalho Chehab" Date: Mon, 31 Mar 2014 00:23:35 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 009/200] [media] dib8000: make 32 bits read atomic In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.56-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Mauro Carvalho Chehab commit 5ac64ba12aca3bef18e61c866583155a3bbf81c4 upstream. As the dvb-frontend kthread can be called anytime, it can race with some get status ioctl. So, it seems better to avoid one to race with the other while reading a 32 bits register. I can't see any other reason for having a mutex there at I2C, except to provide such kind of protection, as the I2C core already has a mutex to protect I2C transfers. Note: instead of this approach, it could eventually remove the dib8000 specific mutex for it, and either group the 4 ops into one xfer or to manually control the I2C mutex. The main advantage of the current approach is that the changes are smaller and more puntual. Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Mauro Carvalho Chehab Acked-by: Patrick Boettcher [bwh: Backported to 3.2: adjust filename] Signed-off-by: Ben Hutchings --- drivers/media/dvb/frontends/dib8000.c | 33 +++++++++++++++++++++++++-------- 1 file changed, 25 insertions(+), 8 deletions(-) --- a/drivers/media/dvb/frontends/dib8000.c +++ b/drivers/media/dvb/frontends/dib8000.c @@ -114,15 +114,10 @@ static u16 dib8000_i2c_read16(struct i2c return ret; } -static u16 dib8000_read_word(struct dib8000_state *state, u16 reg) +static u16 __dib8000_read_word(struct dib8000_state *state, u16 reg) { u16 ret; - if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) { - dprintk("could not acquire lock"); - return 0; - } - state->i2c_write_buffer[0] = reg >> 8; state->i2c_write_buffer[1] = reg & 0xff; @@ -140,6 +135,21 @@ static u16 dib8000_read_word(struct dib8 dprintk("i2c read error on %d", reg); ret = (state->i2c_read_buffer[0] << 8) | state->i2c_read_buffer[1]; + + return ret; +} + +static u16 dib8000_read_word(struct dib8000_state *state, u16 reg) +{ + u16 ret; + + if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) { + dprintk("could not acquire lock"); + return 0; + } + + ret = __dib8000_read_word(state, reg); + mutex_unlock(&state->i2c_buffer_lock); return ret; @@ -149,8 +159,15 @@ static u32 dib8000_read32(struct dib8000 { u16 rw[2]; - rw[0] = dib8000_read_word(state, reg + 0); - rw[1] = dib8000_read_word(state, reg + 1); + if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) { + dprintk("could not acquire lock"); + return 0; + } + + rw[0] = __dib8000_read_word(state, reg + 0); + rw[1] = __dib8000_read_word(state, reg + 1); + + mutex_unlock(&state->i2c_buffer_lock); return ((rw[0] << 16) | (rw[1])); }