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 12:09, Joao Martins 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.
> 
To be clear by "then a bigger patch" I actually meant that the
EXPORT_SYMBOL_NS()/MODULE_NS_IMPORT() would be a separate patch not included
this series. For this series I would just use EXPORT_SYMBOL().

> The struct_size, yeah, should be a separate patch much like commit 7d18dd75a8af
> ("device-dax/kmem: use struct_size()").
> 
This cleanup would still be included as a predecessor patch, as I will be
touching this area in this patch.

> minor comment below on your snippet.
> 
>>
>> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
>> index 6cc4da4c713d..67ab7e05b340 100644
>> --- a/drivers/dax/bus.c
>> +++ b/drivers/dax/bus.c
>> @@ -134,6 +134,12 @@ static bool is_static(struct dax_region *dax_region)
>>         return (dax_region->res.flags & IORESOURCE_DAX_STATIC) != 0;
>>  }
>>
>> +bool static_dev_dax(struct dev_dax *dev_dax)
>> +{
>> +       return is_static(dev_dax->region);
>> +}
>> +EXPORT_SYMBOL_NS_GPL(static_dev_dax, DAX);
>> +
>>  static u64 dev_dax_size(struct dev_dax *dev_dax)
>>  {
>>         u64 size = 0;
>> @@ -363,6 +369,8 @@ void kill_dev_dax(struct dev_dax *dev_dax)
>>
>>         kill_dax(dax_dev);
>>         unmap_mapping_range(inode->i_mapping, 0, 0, 1);
>> +       if (static_dev_dax(dev_dax))
>> +               dev_dax->pgmap = NULL;
>>  }
> 
> Here you probably meant !static_dev_dax() per my patch.
> 
>>  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).
> 
>>         for (i = 0; i < dev_dax->nr_range; i++) {
>>                 struct range *range = &dev_dax->ranges[i].range;
>>
>> -               if (!devm_request_mem_region(dev, range->start,
>> -                                       range_len(range), dev_name(dev))) {
>> -                       dev_warn(dev, "mapping%d: %#llx-%#llx could
>> not reserve range\n",
>> -                                       i, range->start, range->end);
>> -                       return -EBUSY;
>> -               }
>> -               /* don't update the range for static pgmap */
>> -               if (!dev_dax->pgmap)
>> -                       pgmap->ranges[i] = *range;
>> +               if (devm_request_mem_region(dev, range->start, range_len(range),
>> +                                           dev_name(dev)))
>> +                       continue;
>> +               dev_warn(dev,
>> +                        "mapping%d: %#llx-%#llx could not reserve range\n", i,
>> +                        range->start, range->end);
>> +               return -EBUSY;
>>         }
>>
>>         pgmap->type = MEMORY_DEVICE_GENERIC;
>> @@ -473,3 +485,4 @@ MODULE_LICENSE("GPL v2");
>>  module_init(dax_init);
>>  module_exit(dax_exit);
>>  MODULE_ALIAS_DAX_DEVICE(0);
>> +MODULE_IMPORT_NS(DAX);
>