Re: negative count with static key devmap_managed_key

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:

> Hi Christoph,
>
> commit 6f42193fd86e ("memremap: don't use a separate devm action for
> devmap_managed_enable_get") changed the static key updates such that we
> are now calling	devmap_managed_enable_put() without doing the equivalent
> devmap_managed_enable_get().
>
> devmap_managed_enable_get() is only called for MEMORY_DEVICE_PRIVATE and
> MEMORY_DEVICE_FS_DAX, But memunmap_pages() get called for other pgmap
> types too. This result in the below. I can recreate this by repeatedly
> switching between system-ram and devdax mode for devdax namespace. 
>
>


mm/memremap.c | 19 +++++++++++++++----

modified   mm/memremap.c
@@ -158,6 +158,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
 {
 	unsigned long pfn;
 	int i;
+	bool need_devmap_managed = false;
+
+	switch (pgmap->type) {
+	case MEMORY_DEVICE_PRIVATE:
+	case MEMORY_DEVICE_FS_DAX:
+		need_devmap_managed = true;
+		break;
+	default:
+		break;
+	}
 
 	dev_pagemap_kill(pgmap);
 	for (i = 0; i < pgmap->nr_range; i++)
@@ -169,7 +179,8 @@ void memunmap_pages(struct dev_pagemap *pgmap)
 		pageunmap_range(pgmap, i);
 
 	WARN_ONCE(pgmap->altmap.alloc, "failed to free all reserved pages\n");
-	devmap_managed_enable_put();
+	if (need_devmap_managed)
+		devmap_managed_enable_put();
 }
 EXPORT_SYMBOL_GPL(memunmap_pages);
 
@@ -307,7 +318,7 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 		.pgprot = PAGE_KERNEL,
 	};
 	const int nr_range = pgmap->nr_range;
-	bool need_devmap_managed = true;
+	bool need_devmap_managed = false;
 	int error, i;
 
 	if (WARN_ONCE(!nr_range, "nr_range must be specified\n"))
@@ -327,6 +338,7 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 			WARN(1, "Missing owner\n");
 			return ERR_PTR(-EINVAL);
 		}
+		need_devmap_managed = true;
 		break;
 	case MEMORY_DEVICE_FS_DAX:
 		if (!IS_ENABLED(CONFIG_ZONE_DEVICE) ||
@@ -334,13 +346,12 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 			WARN(1, "File system DAX not supported\n");
 			return ERR_PTR(-EINVAL);
 		}
+		need_devmap_managed = true;
 		break;
 	case MEMORY_DEVICE_GENERIC:
-		need_devmap_managed = false;
 		break;
 	case MEMORY_DEVICE_PCI_P2PDMA:
 		params.pgprot = pgprot_noncached(params.pgprot);
-		need_devmap_managed = false;
 		break;
 	default:
 		WARN(1, "Invalid pgmap type %d\n", pgmap->type);
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