On 04/07/12 07:50, Konstantin Belousov wrote:
Hello,
there seems to be a problem with device attach sequence offered by newbus.
Basically, when device attach method is executing, device is not fully
initialized yet. Also the device state in the newbus part of the world
is DS_ALIVE. There is definitely no shattering news in the statements,
but drivers that e.g. create devfs node to communicate with consumers
are prone to a race.
If /dev node is created inside device attach method, then usermode
can start calling cdevsw methods before device fully initialized itself.
Even more, if device tries to use newbus helpers in cdevsw methods,
like device_busy(9), then panic occurs "called for unatteched device".
I get reports from users about this issues, to it is not something
that only could happen.
I propose to add DEVICE_AFTER_ATTACH() driver method, to be called
from newbus right after device attach finished and newbus considers
the device fully initialized. Driver then could create devfs node
in the after_attach method instead of attach. Please see the patch below.
Something like this would also be very useful for drivers that need to
interact across the device tree, if newbus called it only after all
drivers have been attached. Drivers that need to see other potentially
attached drivers now need to do some hacks with SYSINIT. Would it be
possible to do this? I don't think it changes the functionality you need.
-Nathan
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