On Wed, Jul 08, 2015 at 03:59:12PM +0300, Vladimir Zapolskiy wrote: > of_find_i2c_adapter_by_node() call requires quite often missing > put_device(), and i2c_put_adapter() releases a device locked by > i2c_get_adapter() only. In general module_put(adapter->owner) and > put_device(dev) are not interchangeable. > > This is a common error reproduction scenario as a result of the > misusage described above (for clearness this is run on iMX6 platform > with HDMI and I2C bus drivers compiled as kernel modules): > > root@mx6q:~# lsmod | grep i2c > i2c_imx 10213 0 > root@mx6q:~# lsmod | grep dw_hdmi_imx > dw_hdmi_imx 3631 0 > dw_hdmi 11846 1 dw_hdmi_imx > imxdrm 8674 3 dw_hdmi_imx,imx_ipuv3_crtc,imx_ldb > drm_kms_helper 113765 5 dw_hdmi,imxdrm,imx_ipuv3_crtc,imx_ldb > root@mx6q:~# rmmod dw_hdmi_imx > root@mx6q:~# lsmod | grep i2c > i2c_imx 10213 -1 > > ^^^^^ > > root@mx6q:~# rmmod i2c_imx > rmmod: ERROR: Module i2c_imx is in use > > To fix existing users of these interfaces and to avoid any further > confusion and misusage in future, add one more interface > of_get_i2c_adapter_by_node(), it is similar to i2c_get_adapter() in > sense that an I2C bus device driver found and locked by user can be > correctly unlocked by i2c_put_adapter(). > > Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@xxxxxxxxxx> > --- > The change is based on RFC http://www.spinics.net/lists/linux-i2c/msg20257.html > > * added new exported function declaration in include/linux/i2c.h > * added put_device(dev) call right inside of_get_i2c_adapter_by_node() > * corrected authorship of the change > > drivers/i2c/i2c-core.c | 20 ++++++++++++++++++++ > include/linux/i2c.h | 6 ++++++ > 2 files changed, 26 insertions(+) > > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c > index 069a41f..0d902ab 100644 > --- a/drivers/i2c/i2c-core.c > +++ b/drivers/i2c/i2c-core.c > @@ -1356,6 +1356,26 @@ struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node) > return i2c_verify_adapter(dev); > } > EXPORT_SYMBOL(of_find_i2c_adapter_by_node); > + > +struct i2c_adapter *of_get_i2c_adapter_by_node(struct device_node *node) > +{ > + struct device *dev; > + struct i2c_adapter *adapter; > + > + dev = bus_find_device(&i2c_bus_type, NULL, node, > + of_dev_node_match); > + if (!dev) > + return NULL; > + > + adapter = i2c_verify_adapter(dev); > + if (adapter && !try_module_get(adapter->owner)) > + adapter = NULL; > + > + put_device(dev); I don't think this is correct. Users still need to keep a reference to the device, otherwise it can simply disappear even if the module stays around (think sysfs bind/unbind attributes). Looking at i2c_put_adapter() it seems like it would need to do more than just drop the module reference. Then again, that probably means that we need to add a get_device() somewhere in i2c_get_adapter() to balance the put_device() in i2c_put_adapter(). Thierry
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