Hi!
On 05/17/2013 04:42 PM, ext Alan Stern wrote:
i2c: suppress lockdep warning on delete_device
Since commit 846f99749ab68bbc7f75c74fec305de675b1a1bf the following lockdep
warning is thrown in case i2c device is removed (via delete_device sysfs
attribute) which contains subdevices (e.g. i2c multiplexer):
Can you explain this in a little more detail? Exactly what does the
delete_device attribute do, when called for device D?
That is, what does a write to /sys/bus/i2c/devices/D/delete_device do?
Like USB with its hubs, I2C structure could be tree-like, with I2C multiplexers.
delete_device attribute removes I2C device from the subsystem, which is usually not
a problem, except the case when device is a multiplexer and sub-devices should be
removed first. Here we have the problem: holding a "s_active" lock on
"delete_device" attribute of a parent (multiplexer) we need to delete children, but
they were created with the same static attribute "delete_device".
The safety of this operation is exactly the same as in USB case... Any more clever
lockdep annotation is exactly not so easy...
--
Best regards,
Alexander Sverdlin.
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