drivers/base/devres: introduce devm_release_action()

Patch series "mm/devm_memremap_pages: Fix page release race", v2.

Logan audited the devm_memremap_pages() shutdown path and noticed that
it was possible to proceed to arch_remove_memory() before all potential
page references have been reaped.

Introduce a new ->cleanup() callback to do the work of waiting for any
straggling page references and then perform the percpu_ref_exit() in
devm_memremap_pages_release() context.

For p2pdma this involves some deeper reworks to reference count
resources on a per-instance basis rather than a per pci-device basis.  A
modified genalloc api is introduced to convey a driver-private pointer
through gen_pool_{alloc,free}() interfaces.  Also, a
devm_memunmap_pages() api is introduced since p2pdma does not
auto-release resources on a setup failure.

The dax and pmem changes pass the nvdimm unit tests, and the p2pdma
changes should now pass testing with the pci_p2pdma_release() fix.
Jrme, how does this look for HMM?

This patch (of 6):

The devm_add_action() facility allows a resource allocation routine to
add custom devm semantics.  One such user is devm_memremap_pages().

There is now a need to manually trigger
devm_memremap_pages_release().  Introduce devm_release_action() so the
release action can be triggered via a new devm_memunmap_pages() api in a
follow-on change.

Link: http://lkml.kernel.org/r/155727336530.292046.2926860263201336366.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/base/devres.c

@@ -755,10 +755,32 @@ void devm_remove_action(struct device *dev, void (*action)(void *), void *data)
 
 	WARN_ON(devres_destroy(dev, devm_action_release, devm_action_match,
 			       &devres));
-
 }
 EXPORT_SYMBOL_GPL(devm_remove_action);
 
+/**
+ * devm_release_action() - release previously added custom action
+ * @dev: Device that owns the action
+ * @action: Function implementing the action
+ * @data: Pointer to data passed to @action implementation
+ *
+ * Releases and removes instance of @action previously added by
+ * devm_add_action().  Both action and data should match one of the
+ * existing entries.
+ */
+void devm_release_action(struct device *dev, void (*action)(void *), void *data)
+{
+	struct action_devres devres = {
+		.data = data,
+		.action = action,
+	};
+
+	WARN_ON(devres_release(dev, devm_action_release, devm_action_match,
+			       &devres));
+
+}
+EXPORT_SYMBOL_GPL(devm_release_action);
+
 /*
  * Managed kmalloc/kfree
  */

include/linux/device.h

@@ -713,6 +713,7 @@ void __iomem *devm_of_iomap(struct device *dev,
 /* allows to add/remove a custom action to devres stack */
 int devm_add_action(struct device *dev, void (*action)(void *), void *data);
 void devm_remove_action(struct device *dev, void (*action)(void *), void *data);
+void devm_release_action(struct device *dev, void (*action)(void *), void *data);
 
 static inline int devm_add_action_or_reset(struct device *dev,
 					   void (*action)(void *), void *data)