Hi Thierry, On 08.07.2015 16:11, Thierry Reding wrote: > 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(). it makes sense for me, thanks for momentary review. I'm hesitating to add put_device(dev) to i2c_put_adapter() etc. in this series though. After development and testing I would like to send another preceding independent change updating i2c_get_adapter(), i2c_put_adapter() and clients (or if you wish you can do it), then I'll rebase 01/10 on top of it, the rest most probably is unchanged. -- With best wishes, Vladimir -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
