Re: [PATCH v4 06/14] device-dax: ensure dev_dax->pgmap is valid for dynamic devices

[Joao Martins <joao.m.martins@oracle.com>]

On 11/5/21 16:46, Dan Williams wrote:
> On Fri, Nov 5, 2021 at 5:10 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>> On 11/5/21 00:31, Dan Williams wrote:
>>> On Fri, Aug 27, 2021 at 7:59 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>>>>
>>>> Right now, only static dax regions have a valid @pgmap pointer in its
>>>> struct dev_dax. Dynamic dax case however, do not.
>>>>
>>>> In preparation for device-dax compound devmap support, make sure that
>>>> dev_dax pgmap field is set after it has been allocated and initialized.
>>>>
>>>> dynamic dax device have the @pgmap is allocated at probe() and it's
>>>> managed by devm (contrast to static dax region which a pgmap is provided
>>>> and dax core kfrees it). So in addition to ensure a valid @pgmap, clear
>>>> the pgmap when the dynamic dax device is released to avoid the same
>>>> pgmap ranges to be re-requested across multiple region device reconfigs.
>>>>
>>>> Suggested-by: Dan Williams <dan.j.williams@intel.com>
>>>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>>>> ---
>>>>  drivers/dax/bus.c    | 8 ++++++++
>>>>  drivers/dax/device.c | 2 ++
>>>>  2 files changed, 10 insertions(+)
>>>>
>>>> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
>>>> index 6cc4da4c713d..49dbff9ba609 100644
>>>> --- a/drivers/dax/bus.c
>>>> +++ b/drivers/dax/bus.c
>>>> @@ -363,6 +363,14 @@ void kill_dev_dax(struct dev_dax *dev_dax)
>>>>
>>>>         kill_dax(dax_dev);
>>>>         unmap_mapping_range(inode->i_mapping, 0, 0, 1);
>>>> +
>>>> +       /*
>>>> +        * Dynamic dax region have the pgmap allocated via dev_kzalloc()
>>>> +        * and thus freed by devm. Clear the pgmap to not have stale pgmap
>>>> +        * ranges on probe() from previous reconfigurations of region devices.
>>>> +        */
>>>> +       if (!is_static(dev_dax->region))
>>>> +               dev_dax->pgmap = NULL;
>>>>  }
>>>>  EXPORT_SYMBOL_GPL(kill_dev_dax);
>>>>
>>>> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
>>>> index 0b82159b3564..6e348b5f9d45 100644
>>>> --- a/drivers/dax/device.c
>>>> +++ b/drivers/dax/device.c
>>>> @@ -426,6 +426,8 @@ int dev_dax_probe(struct dev_dax *dev_dax)
>>>>         }
>>>>
>>>>         pgmap->type = MEMORY_DEVICE_GENERIC;
>>>> +       dev_dax->pgmap = pgmap;
>>>
>>> So I think I'd rather see a bigger patch that replaces some of the
>>> implicit dev_dax->pgmap == NULL checks with explicit is_static()
>>> checks. Something like the following only compile and boot tested...
>>> Note the struct_size() change probably wants to be its own cleanup,
>>> and the EXPORT_SYMBOL_NS_GPL(..., DAX) probably wants to be its own
>>> patch converting over the entirety of drivers/dax/. Thoughts?
>>>
>> It's a good idea. Certainly the implicit pgmap == NULL made it harder
>> than the necessary to find where the problem was. So turning those checks
>> into explicit checks that differentiate static vs dynamic dax will help
>>
>> With respect to this series converting those pgmap == NULL is going to need
>> to made me export the symbol (provided dax core and dax device can be built
>> as modules). So I don't know how this can be a patch converting entirety of
>> dax. Perhaps you mean that I would just EXPORT_SYMBOL() and then a bigger
>> patch introduces the MODULE_NS_IMPORT() And EXPORT_SYMBOL_NS*() separately.
> 
> Yeah, either a lead-in patch to do the conversion, or a follow on to
> convert everything after the fact. Either way works for me, but I have
> a small preference for the lead-in patch.
> 

The one reason I am leaning towards the after the fact conversion, is that the
addition of a new exported symbol looks unrelated to a drivers/dax wide conversion
to namespaced symbols. Looks like a separate cleanup on top of this series, as
opposed to a dependency cleanup.

>>>  EXPORT_SYMBOL_GPL(kill_dev_dax);
>>>
>>> diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
>>> index 1e946ad7780a..4acdfee7dd59 100644
>>> --- a/drivers/dax/bus.h
>>> +++ b/drivers/dax/bus.h
>>> @@ -48,6 +48,7 @@ int __dax_driver_register(struct dax_device_driver *dax_drv,
>>>         __dax_driver_register(driver, THIS_MODULE, KBUILD_MODNAME)
>>>  void dax_driver_unregister(struct dax_device_driver *dax_drv);
>>>  void kill_dev_dax(struct dev_dax *dev_dax);
>>> +bool static_dev_dax(struct dev_dax *dev_dax);
>>>
>>>  #if IS_ENABLED(CONFIG_DEV_DAX_PMEM_COMPAT)
>>>  int dev_dax_probe(struct dev_dax *dev_dax);
>>> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
>>> index dd8222a42808..87507aff2b10 100644
>>> --- a/drivers/dax/device.c
>>> +++ b/drivers/dax/device.c
>>> @@ -398,31 +398,43 @@ int dev_dax_probe(struct dev_dax *dev_dax)
>>>         void *addr;
>>>         int rc, i;
>>>
>>> -       pgmap = dev_dax->pgmap;
>>> -       if (dev_WARN_ONCE(dev, pgmap && dev_dax->nr_range > 1,
>>> -                       "static pgmap / multi-range device conflict\n"))
>>> +       if (static_dev_dax(dev_dax) && dev_dax->nr_range > 1) {
>>> +               dev_warn(dev, "static pgmap / multi-range device conflict\n");
>>>                 return -EINVAL;
>>> +       }
>>>
>>> -       if (!pgmap) {
>>> -               pgmap = devm_kzalloc(dev, sizeof(*pgmap) + sizeof(struct range)
>>> -                               * (dev_dax->nr_range - 1), GFP_KERNEL);
>>> +       if (static_dev_dax(dev_dax)) {
>>> +               pgmap = dev_dax->pgmap;
>>> +       } else {
>>> +               if (dev_dax->pgmap) {
>>> +                       dev_warn(dev,
>>> +                                "dynamic-dax with pre-populated page map!?\n");
>>> +                       return -EINVAL;
>>> +               }
>>> +               pgmap = devm_kzalloc(
>>> +                       dev, struct_size(pgmap, ranges, dev_dax->nr_range - 1),
>>> +                       GFP_KERNEL);
>>>                 if (!pgmap)
>>>                         return -ENOMEM;
>>>                 pgmap->nr_range = dev_dax->nr_range;
>>> +               dev_dax->pgmap = pgmap;
>>> +               for (i = 0; i < dev_dax->nr_range; i++) {
>>> +                       struct range *range = &dev_dax->ranges[i].range;
>>> +
>>> +                       pgmap->ranges[i] = *range;
>>> +               }
>>>         }
>>>
>> This code move is probably not needed unless your point is to have a more clear
>> separation on what's initialization versus the mem region request (that's
>> applicable to both dynamic and static).
> 
> It was more of an RFC cleanup idea and yes, should be its own patch if
> you think it helps make the init path clearer.
> 
OK.