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

[Dan Williams <dan.j.williams@intel.com>]

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?


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;
 }
 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;
+               }
        }

        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);



> +
>         addr = devm_memremap_pages(dev, pgmap);
>         if (IS_ERR(addr))
>                 return PTR_ERR(addr);
> --
> 2.17.1
>