[openib-general][PATCH][kdapl]: inc/dec module ref count

[Guy German]

Hi,

James Lentini <mailto:jlentini at netapp.com> wrote:
> On Sun, 31 Jul 2005, Muli Ben-Yehuda wrote:
> 
>> On Sun, Jul 31, 2005 at 06:08:11PM +0300, Guy German wrote:
>>> Hi Muli,
>>> 
>>> Wouldn't it be solved by moving the try_module_get call to the
>>> beginning of the dapl_ia_open function ?
>> 
>> No. Even if it's theoretically the first line in the function, the
>> compiler can and will create a function prologue that will run before
>> you raise the reference count (same thing with decrementing the ref
>> count at module unload time and the function epilogue). You must do
>> module reference counting before executing even one instruction from
>> the module. 
>> 
>>> You are right - try_module_get() can fail when the module is not
>>> ready to be entered. should be something like:
>>> + if (!try_module_get(THIS_MODULE))
>>> +	return -EBUSY;
>> 
>> Yes - but at the caller, not callee.
> 
> Putting this in the caller (i.e. dat_ia_open and dat_ia_close) does
> sound like a better option. 

Sounds good to me too.

> 
> Guy, can you investigate why the ib_mthca module doesn't have a
> reference count and see if it relates to hotplug? I think
> kdapl_ib and
> ib_mthca should have the same policy regarding this issue.

As I understand, consumers are working over ib_core and not over ib_mthca
directly. So, if (from a hotplug reason) ib_mthca goes down, ib_core consumers 
can get notified of the event, by an upcall.

If you take this model to dapl, I think it would influence the way dapl consumers
need to do things (like registering an upcall and know what to do in case kdapl_ib
is down). 

I also don't know how many consumers really need "dapl hotplug"...

Guy