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[HMM v14 01/16] mm/free_hot_cold_page: catch ZONE_DEVICE pages

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Catch page from ZONE_DEVICE in free_hot_cold_page(). This should never
happen as ZONE_DEVICE page must always have an elevated refcount.

This is safety-net to catch any refcounting issues in a sane way for any
ZONE_DEVICE pages.

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 mm/page_alloc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0fbfead..09b2630 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2435,6 +2435,16 @@ void free_hot_cold_page(struct page *page, bool cold)
 	unsigned long pfn = page_to_pfn(page);
 	int migratetype;
 
+	/*
+	 * This should never happen ! Page from ZONE_DEVICE always must have an
+	 * active refcount. Complain about it and try to restore the refcount.
+	 */
+	if (is_zone_device_page(page)) {
+		VM_BUG_ON_PAGE(is_zone_device_page(page), page);
+		page_ref_inc(page);
+		return;
+	}
+
 	if (!free_pcp_prepare(page))
 		return;
 
-- 
2.4.3

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[HMM v14 00/16] HMM (Heterogeneous Memory Management) v14 Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:40 +0100
  [HMM v14 12/16] mm/hmm/migrate: add new boolean copy flag to migratepage() callback Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:40 +0100
  [HMM v14 01/16] mm/free_hot_cold_page: catch ZONE_DEVICE pages Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 06/16] mm/ZONE_DEVICE/x86: add support for un-addressable device memory Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 03/16] mm/ZONE_DEVICE/devmem_pages_remove: allow early removal of device memory Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 13/16] mm/hmm/migrate: new memory migration helper for use with device memory v2 Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 07/16] mm/hmm: heterogeneous memory management (HMM for short) Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 05/16] mm/ZONE_DEVICE/unaddressable: add support for un-addressable device memory Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
    Re: [HMM v14 05/16] mm/ZONE_DEVICE/unaddressable: add support for  un-addressable device memory Dave Hansen <dave.hansen@intel.com> - 2016-12-08 17:30 +0100
      Re: [HMM v14 05/16] mm/ZONE_DEVICE/unaddressable: add support for  un-addressable device memory Jerome Glisse <jglisse@redhat.com> - 2016-12-08 17:50 +0100
        Re: [HMM v14 05/16] mm/ZONE_DEVICE/unaddressable: add support for  un-addressable device memory Dave Hansen <dave.hansen@intel.com> - 2016-12-08 21:10 +0100
          Re: [HMM v14 05/16] mm/ZONE_DEVICE/unaddressable: add support for  un-addressable device memory Jerome Glisse <jglisse@redhat.com> - 2016-12-08 21:40 +0100
  [HMM v14 02/16] mm/memory/hotplug: convert device bool to int to allow for more flags v2 Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 16/16] mm/hmm/devmem: dummy HMM device as an helper for ZONE_DEVICE memory Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 04/16] mm/ZONE_DEVICE/free-page: callback when page is freed Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 15/16] mm/hmm/devmem: device driver helper to hotplug ZONE_DEVICE memory Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 10/16] mm/hmm/mirror: device page fault handler Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 08/16] mm/hmm/mirror: mirror process address space on device with HMM helpers Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 14/16] mm/hmm/migrate: optimize page map once in vma being migrated Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100
  [HMM v14 09/16] mm/hmm/mirror: helper to snapshot CPU page table Jérôme Glisse <jglisse@redhat.com> - 2016-12-08 16:50 +0100

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