On Wed, Jul 08, 2015 at 04:31:37PM +0300, Vladimir Zapolskiy wrote: > 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. I think that would make sense, yes. Thierry
Attachment:
pgpAE1lqtiVyK.pgp
Description: PGP signature
