On 07/17/2014 09:06 AM, Hefty, Sean wrote:
>> On 7/17/2014 9:01 AM, Devesh Sharma wrote:
>>> If verndor driver is attempted for removal while xprtrdma still has an
>>> active mount, the removal of driver may never complete and can cause
>>> unseen races or in worst case system crash.
>>>
>>> To solve this, xprtrdma module should get reference of struct ib_device
>>> structure for every mount. Reference is taken after local device address
>>> resolution is completed successfuly.
>>>
>>> reference to the struct ib_device pointer is put just before cm_id
>> destruction.
>>>
>>> Signed-off-by: Devesh Sharma <devesh.sha...@emulex.com>
>>
>> This seems like an issue with the rdma-cm or rdma core, not xprtrdma. I
>> see that user rdma applications cause a ref on the provider module here
>> in ib_uverbs_open():
>>
>> if (!try_module_get(dev->ib_dev->owner)) {
>> ret = -ENODEV;
>> goto err;
>>
>>
>> Maybe kernel applications that allocate device resources should cause a
>> ref on the provider's module.
>>
>> Sean/Roland, is there some history here as to how rdma provider module
>> removal should be handled?
>
> The kernel modules should are not expected to access the rdma devices after
> their remove device callback has been invoked. The rdma cm basically
> forwards the device removal on a per id basis. Apps are expected to destroy
> the id after receiving that callback. The rdma cm should block in the remove
> device call until all id's associated with the removed device have been
> destroyed.
So the rdma cm is expected to increase the driver reference count
(try_module_get) for each new cm id, then deference count (module_put) when cm
id is destroyed?
> - Sean
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