Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752244AbdCSRRq (ORCPT ); Sun, 19 Mar 2017 13:17:46 -0400 Received: from mail-it0-f67.google.com ([209.85.214.67]:36062 "EHLO mail-it0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752178AbdCSRRn (ORCPT ); Sun, 19 Mar 2017 13:17:43 -0400 MIME-Version: 1.0 In-Reply-To: <20170319125039.GA23385@singhal-Inspiron-5558> References: <20170319125039.GA23385@singhal-Inspiron-5558> From: Gargi Sharma Date: Sun, 19 Mar 2017 22:44:38 +0530 Message-ID: Subject: Re: [Outreachy kernel] [PATCH v5] staging: Use buf_lock instead of mlock and Refactor code To: simran singhal Cc: Lars-Peter Clausen , Michael Hennerich , Jonathan Cameron , Hartmut Knaack , Peter Meerwald-Stadler , Greg Kroah-Hartman , linux-iio@vger.kernel.org, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org, outreachy-kernel@googlegroups.com Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5229 Lines: 138 On Sun, Mar 19, 2017 at 6:20 PM, simran singhal wrote: > The IIO subsystem is redefining iio_dev->mlock to be used by > the IIO core only for protecting device operating mode changes. > ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes. > > In this driver, mlock was being used to protect hardware state > changes. Replace it with buf_lock in the devices global data. > > As buf_lock protects both the adis16060_spi_write() and > adis16060_spi_read() functions and both are always called in > pair. First write, then read. Thus, refactor the code to have > one single function adis16060_spi_write_than_read() which is > protected by the existing buf_lock. > > Signed-off-by: simran singhal > --- > > v5: > -Rename val in adis16060_spi_write_than_read() to conf. > -Rename val2 in adis16060_spi_write_than_read() to val. > -Corrected Checkpatch issues. > -Removed goto from adis16060_read_raw(). > > > drivers/staging/iio/gyro/adis16060_core.c | 42 ++++++++++++------------------- > 1 file changed, 16 insertions(+), 26 deletions(-) > > diff --git a/drivers/staging/iio/gyro/adis16060_core.c b/drivers/staging/iio/gyro/adis16060_core.c > index c9d46e7..0f12492 100644 > --- a/drivers/staging/iio/gyro/adis16060_core.c > +++ b/drivers/staging/iio/gyro/adis16060_core.c > @@ -40,25 +40,20 @@ struct adis16060_state { > > static struct iio_dev *adis16060_iio_dev; > > -static int adis16060_spi_write(struct iio_dev *indio_dev, u8 val) > +static int adis16060_spi_write_than_read(struct iio_dev *indio_dev, > + u8 conf, u16 *val) > { > int ret; > struct adis16060_state *st = iio_priv(indio_dev); > > mutex_lock(&st->buf_lock); > - st->buf[2] = val; /* The last 8 bits clocked in are latched */ > + st->buf[2] = conf; /* The last 8 bits clocked in are latched */ > ret = spi_write(st->us_w, st->buf, 3); > - mutex_unlock(&st->buf_lock); > > - return ret; > -} > - > -static int adis16060_spi_read(struct iio_dev *indio_dev, u16 *val) > -{ > - int ret; > - struct adis16060_state *st = iio_priv(indio_dev); > - > - mutex_lock(&st->buf_lock); > + if (ret < 0) { > + mutex_unlock(&st->buf_lock); > + return ret; > + } > > ret = spi_read(st->us_r, st->buf, 3); > > @@ -69,8 +64,8 @@ static int adis16060_spi_read(struct iio_dev *indio_dev, u16 *val) > */ > if (!ret) > *val = ((st->buf[0] & 0x3) << 12) | > - (st->buf[1] << 4) | > - ((st->buf[2] >> 4) & 0xF); > + (st->buf[1] << 4) | > + ((st->buf[2] >> 4) & 0xF); > mutex_unlock(&st->buf_lock); > > return ret; > @@ -83,20 +78,19 @@ static int adis16060_read_raw(struct iio_dev *indio_dev, > { > u16 tval = 0; > int ret; > + struct adis16060_state *st = iio_priv(indio_dev); > > switch (mask) { > case IIO_CHAN_INFO_RAW: > /* Take the iio_dev status lock */ > - mutex_lock(&indio_dev->mlock); > - ret = adis16060_spi_write(indio_dev, chan->address); > + mutex_lock(&st->buf_lock); > + ret = adis16060_spi_write_than_read(indio_dev, > + chan->address, &tval); > if (ret < 0) > - goto out_unlock; > + mutex_unlock(&st->buf_lock); > + return ret; > > - ret = adis16060_spi_read(indio_dev, &tval); > - if (ret < 0) > - goto out_unlock; > - > - mutex_unlock(&indio_dev->mlock); > + mutex_unlock(&st->buf_lock); > *val = tval; > return IIO_VAL_INT; > case IIO_CHAN_INFO_OFFSET: > @@ -110,10 +104,6 @@ static int adis16060_read_raw(struct iio_dev *indio_dev, > } > > return -EINVAL; > - > -out_unlock: > - mutex_unlock(&indio_dev->mlock); > - return ret; > } > Hey Simran, I'm another Outreachy aspirant and I'm trying to work through a similar patch in another driver. Can you please explain to me how you are avoiding nested locks here? From what I understand, the function adis16060_read_raw call a lock on &st->buf_lock and then you call the function adis16060_spi_write_than_read which again tries to get hold of the same lock. Isn't this a deadlock situation? Please let me know if my understanding is incorrect. Thank you! Gargi > static const struct iio_info adis16060_info = { > -- > 2.7.4 > > -- > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group. > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com. > To post to this group, send email to outreachy-kernel@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/20170319125039.GA23385%40singhal-Inspiron-5558. > For more options, visit https://groups.google.com/d/optout.