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Mon, 17 Aug 2026 14:11:37 -0700 (PDT) From: Taha Ed-Dafili <0rayn.dev@gmail.com> To: jic23@kernel.org, lars@metafoo.de Cc: Michael.Hennerich@analog.com, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, dlechner@baylibre.com, nuno.sa@analog.com, andy@kernel.org, skhan@linuxfoundation.org, linux@analog.com, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Taha Ed-Dafili <0rayn.dev@gmail.com> Subject: [PATCH v4 4/6] iio: dac: ad5504: introduce local lock to protect state and spi transfers Date: Mon, 17 Aug 2026 17:11:13 -0400 Message-ID: <20260817211118.21833-5-0rayn.dev@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260817211118.21833-1-0rayn.dev@gmail.com> References: <20260817211118.21833-1-0rayn.dev@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The AD5504 driver currently lacks locking, exposing it to several multi-threading race conditions: 1. The shared DMA-safe SPI transfer buffers (st->data) can be corrupted if multiple threads trigger read_raw or write_raw simultaneously. 2. The ad5504_write_dac_powerdown() routine executes a sequence of back-to-back SPI writes (a CTRL register update followed by a mandatory NOOP). This entire sequence must be atomic. 3. Internal state variables like pwr_down_mask and pwr_down_mode can be read and modified concurrently. Introduce a mutex in the ad5504_state structure and initialize it via devm_mutex_init() in probe. Use the modern scoped guard(mutex) macro at the top-level public IIO callbacks (read_raw, write_raw, and the powerdown attributes) to safely serialize access to the device state and the SPI bus. In ad5504_read_raw() and ad5504_write_raw(), guard(mutex) is scoped to the IIO_CHAN_INFO_RAW case only, since IIO_CHAN_INFO_SCALE merely reads vref_mv, which is fixed at probe time and never modified afterward and therefore needs no serialization. Because guard(mutex) declares a cleanup-scoped variable, it cannot appear directly after a case label; wrap the case body in a compound statement (case IIO_CHAN_INFO_RAW: { ... }) to give it the block scope it requires. Signed-off-by: Taha Ed-Dafili <0rayn.dev@gmail.com> --- Note: The concurrency race conditions addressed in this patch were originally reported by the Sashiko bot: https://sashiko.dev/#/patchset/20260509142047.30302-1-0rayn.dev@gmail.com drivers/iio/dac/ad5504.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/drivers/iio/dac/ad5504.c b/drivers/iio/dac/ad5504.c index 55ce7e49e0e0..87946cdf69e7 100644 --- a/drivers/iio/dac/ad5504.c +++ b/drivers/iio/dac/ad5504.c @@ -7,12 +7,14 @@ #include #include +#include #include #include #include #include #include #include +#include #include #include #include @@ -49,10 +51,12 @@ * @pwr_down_mask: power down mask * @pwr_down_mode: current power down mode * @data: transfer buffer + * @lock: lock to protect state and spi transfers */ struct ad5504_state { struct spi_device *spi; struct regulator *reg; + struct mutex lock; unsigned short vref_mv; unsigned pwr_down_mask; unsigned pwr_down_mode; @@ -103,7 +107,8 @@ static int ad5504_read_raw(struct iio_dev *indio_dev, int ret; switch (m) { - case IIO_CHAN_INFO_RAW: + case IIO_CHAN_INFO_RAW: { + guard(mutex)(&st->lock); ret = ad5504_spi_read(st, chan->address); if (ret < 0) return ret; @@ -111,6 +116,7 @@ static int ad5504_read_raw(struct iio_dev *indio_dev, *val = ret; return IIO_VAL_INT; + } case IIO_CHAN_INFO_SCALE: *val = st->vref_mv; *val2 = chan->scan_type.realbits; @@ -128,11 +134,13 @@ static int ad5504_write_raw(struct iio_dev *indio_dev, struct ad5504_state *st = iio_priv(indio_dev); switch (mask) { - case IIO_CHAN_INFO_RAW: + case IIO_CHAN_INFO_RAW: { + guard(mutex)(&st->lock); if (val >= (1 << chan->scan_type.realbits) || val < 0) return -EINVAL; return ad5504_spi_write(st, chan->address, val); + } default: return -EINVAL; } @@ -148,6 +156,7 @@ static int ad5504_get_powerdown_mode(struct iio_dev *indio_dev, { struct ad5504_state *st = iio_priv(indio_dev); + guard(mutex)(&st->lock); return st->pwr_down_mode; } @@ -156,6 +165,7 @@ static int ad5504_set_powerdown_mode(struct iio_dev *indio_dev, { struct ad5504_state *st = iio_priv(indio_dev); + guard(mutex)(&st->lock); st->pwr_down_mode = mode; return 0; @@ -173,6 +183,7 @@ static ssize_t ad5504_read_dac_powerdown(struct iio_dev *indio_dev, { struct ad5504_state *st = iio_priv(indio_dev); + guard(mutex)(&st->lock); return sysfs_emit(buf, "%d\n", !(st->pwr_down_mask & (1 << chan->channel))); } @@ -185,6 +196,7 @@ static ssize_t ad5504_write_dac_powerdown(struct iio_dev *indio_dev, int ret; struct ad5504_state *st = iio_priv(indio_dev); + guard(mutex)(&st->lock); ret = kstrtobool(buf, &pwr_down); if (ret) return ret; @@ -284,6 +296,10 @@ static int ad5504_probe(struct spi_device *spi) st = iio_priv(indio_dev); + ret = devm_mutex_init(dev, &st->lock); + if (ret) + return ret; + ret = devm_regulator_get_enable_read_voltage(dev, "vcc"); if (ret < 0) return ret; -- 2.55.0