Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752707AbdCSUnO (ORCPT ); Sun, 19 Mar 2017 16:43:14 -0400 Received: from saturn.retrosnub.co.uk ([178.18.118.26]:50813 "EHLO saturn.retrosnub.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752356AbdCSUnK (ORCPT ); Sun, 19 Mar 2017 16:43:10 -0400 Subject: Re: [Outreachy kernel] [PATCH v5] staging: Use buf_lock instead of mlock and Refactor code To: Gargi Sharma , simran singhal References: <20170319125039.GA23385@singhal-Inspiron-5558> Cc: Lars-Peter Clausen , Michael Hennerich , 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 From: Jonathan Cameron Message-ID: <9089c598-7909-1c53-db70-8984edab988c@kernel.org> Date: Sun, 19 Mar 2017 20:43:06 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5865 Lines: 151 On 19/03/17 17:14, Gargi Sharma wrote: > 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. Well spotted. That is indeed the case. Just goes to show how more eyes on code is always a good thing! The locks in read_raw itself should be dropped as we now have a single safe function with the locks inside it being called. Jonathan > > 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. > -- > To unsubscribe from this list: send the line "unsubscribe linux-iio" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >