| Message ID | 20201103193315.3011800-1-robert.hancock@calian.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | hwmon: (pmbus) Add mutex locking for sysfs reads | expand |
On Tue, Nov 3, 2020 at 11:33 AM Robert Hancock <robert.hancock@calian.com> wrote: > > As part of commit a919ba06979a7 ("hwmon: (pmbus) Stop caching register > values"), the update of the sensor value is now triggered directly by the > sensor attribute value being read from sysfs. This created (or at least > made much more likely) a locking issue, since nothing protected the device > page selection from being unexpectedly modified by concurrent reads. If > sensor values on different pages on the same device were being concurrently > read by multiple threads, this could cause spurious read errors due to the > page register not reading back the same value last written, or sensor > values being read from the incorrect page. > > Add locking of the update_lock mutex in pmbus_show_sensor and > pmbus_show_samples so that these cannot result in concurrent reads from the > underlying device. > > Fixes: a919ba06979a7 ("hwmon: (pmbus) Stop caching register values") > Signed-off-by: Robert Hancock <robert.hancock@calian.com> Reviewed-by: Alex Qiu <xqiu@google.com> Hi Robert, Thanks for raising this issue up! - Alex Qiu
On Tue, Nov 03, 2020 at 01:33:15PM -0600, Robert Hancock wrote: > As part of commit a919ba06979a7 ("hwmon: (pmbus) Stop caching register > values"), the update of the sensor value is now triggered directly by the > sensor attribute value being read from sysfs. This created (or at least > made much more likely) a locking issue, since nothing protected the device > page selection from being unexpectedly modified by concurrent reads. If > sensor values on different pages on the same device were being concurrently > read by multiple threads, this could cause spurious read errors due to the > page register not reading back the same value last written, or sensor > values being read from the incorrect page. > > Add locking of the update_lock mutex in pmbus_show_sensor and > pmbus_show_samples so that these cannot result in concurrent reads from the > underlying device. > > Fixes: a919ba06979a7 ("hwmon: (pmbus) Stop caching register values") > Signed-off-by: Robert Hancock <robert.hancock@calian.com> > Reviewed-by: Alex Qiu <xqiu@google.com> Good catch. Applied. Thanks, Guenter > --- > drivers/hwmon/pmbus/pmbus_core.c | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > > diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c > index 170a9f82ca61..b0e2820a2d57 100644 > --- a/drivers/hwmon/pmbus/pmbus_core.c > +++ b/drivers/hwmon/pmbus/pmbus_core.c > @@ -941,12 +941,16 @@ static ssize_t pmbus_show_sensor(struct device *dev, > struct i2c_client *client = to_i2c_client(dev->parent); > struct pmbus_sensor *sensor = to_pmbus_sensor(devattr); > struct pmbus_data *data = i2c_get_clientdata(client); > + ssize_t ret; > > + mutex_lock(&data->update_lock); > pmbus_update_sensor_data(client, sensor); > if (sensor->data < 0) > - return sensor->data; > - > - return snprintf(buf, PAGE_SIZE, "%lld\n", pmbus_reg2data(data, sensor)); > + ret = sensor->data; > + else > + ret = snprintf(buf, PAGE_SIZE, "%lld\n", pmbus_reg2data(data, sensor)); > + mutex_unlock(&data->update_lock); > + return ret; > } > > static ssize_t pmbus_set_sensor(struct device *dev, > @@ -2012,8 +2016,11 @@ static ssize_t pmbus_show_samples(struct device *dev, > int val; > struct i2c_client *client = to_i2c_client(dev->parent); > struct pmbus_samples_reg *reg = to_samples_reg(devattr); > + struct pmbus_data *data = i2c_get_clientdata(client); > > + mutex_lock(&data->update_lock); > val = _pmbus_read_word_data(client, reg->page, 0xff, reg->attr->reg); > + mutex_unlock(&data->update_lock); > if (val < 0) > return val; >
diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c index 170a9f82ca61..b0e2820a2d57 100644 --- a/drivers/hwmon/pmbus/pmbus_core.c +++ b/drivers/hwmon/pmbus/pmbus_core.c @@ -941,12 +941,16 @@ static ssize_t pmbus_show_sensor(struct device *dev, struct i2c_client *client = to_i2c_client(dev->parent); struct pmbus_sensor *sensor = to_pmbus_sensor(devattr); struct pmbus_data *data = i2c_get_clientdata(client); + ssize_t ret; + mutex_lock(&data->update_lock); pmbus_update_sensor_data(client, sensor); if (sensor->data < 0) - return sensor->data; - - return snprintf(buf, PAGE_SIZE, "%lld\n", pmbus_reg2data(data, sensor)); + ret = sensor->data; + else + ret = snprintf(buf, PAGE_SIZE, "%lld\n", pmbus_reg2data(data, sensor)); + mutex_unlock(&data->update_lock); + return ret; } static ssize_t pmbus_set_sensor(struct device *dev, @@ -2012,8 +2016,11 @@ static ssize_t pmbus_show_samples(struct device *dev, int val; struct i2c_client *client = to_i2c_client(dev->parent); struct pmbus_samples_reg *reg = to_samples_reg(devattr); + struct pmbus_data *data = i2c_get_clientdata(client); + mutex_lock(&data->update_lock); val = _pmbus_read_word_data(client, reg->page, 0xff, reg->attr->reg); + mutex_unlock(&data->update_lock); if (val < 0) return val;
As part of commit a919ba06979a7 ("hwmon: (pmbus) Stop caching register values"), the update of the sensor value is now triggered directly by the sensor attribute value being read from sysfs. This created (or at least made much more likely) a locking issue, since nothing protected the device page selection from being unexpectedly modified by concurrent reads. If sensor values on different pages on the same device were being concurrently read by multiple threads, this could cause spurious read errors due to the page register not reading back the same value last written, or sensor values being read from the incorrect page. Add locking of the update_lock mutex in pmbus_show_sensor and pmbus_show_samples so that these cannot result in concurrent reads from the underlying device. Fixes: a919ba06979a7 ("hwmon: (pmbus) Stop caching register values") Signed-off-by: Robert Hancock <robert.hancock@calian.com> --- drivers/hwmon/pmbus/pmbus_core.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)