Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752730AbdCSVPU (ORCPT ); Sun, 19 Mar 2017 17:15:20 -0400 Received: from mail-ua0-f196.google.com ([209.85.217.196]:35207 "EHLO mail-ua0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752356AbdCSVPQ (ORCPT ); Sun, 19 Mar 2017 17:15:16 -0400 MIME-Version: 1.0 In-Reply-To: <9089c598-7909-1c53-db70-8984edab988c@kernel.org> References: <20170319125039.GA23385@singhal-Inspiron-5558> <9089c598-7909-1c53-db70-8984edab988c@kernel.org> From: SIMRAN SINGHAL Date: Mon, 20 Mar 2017 02:45:14 +0530 Message-ID: Subject: Re: [Outreachy kernel] [PATCH v5] staging: Use buf_lock instead of mlock and Refactor code To: Jonathan Cameron Cc: Gargi Sharma , 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 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: 6430 Lines: 165 On Mon, Mar 20, 2017 at 2:13 AM, Jonathan Cameron wrote: > 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! > Jonathan, I have already sent the version 6 of this patch in which I have dropped the locks in the function adis16060_spi_write_than_read and keep the locks of function read_raw as it is. > The locks in read_raw itself should be dropped as we now have a single > safe function with the locks inside it being called. I keep the locks inside read_raw as it is because it will be more safe, if we see in terms of security. If I am wrong here, please correct me. > > 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 >> >