[PATCH v3 16/23] mm/gup: track FOLL_PIN pages

John Hubbard
2019-11-12T00:09:24Z

Add tracking of pages that were pinned via FOLL_PIN.

As mentioned in the FOLL_PIN documentation, callers who effectively set
FOLL_PIN are required to ultimately free such pages via put_user_page().
The effect is similar to FOLL_GET, and may be thought of as "FOLL_GET
for DIO and/or RDMA use".

Pages that have been pinned via FOLL_PIN are identifiable via a
new function call:

bool page_dma_pinned(struct page *page);

What to do in response to encountering such a page, is left to later
patchsets. There is discussion about this in [1].

This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask().

Suggested-by: Jan Kara <jack@suse.cz>
Suggested-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
include/linux/mm.h | 75 ++++++++++++----
include/linux/mmzone.h | 2 +
include/linux/page_ref.h | 10 +++
mm/gup.c | 190 +++++++++++++++++++++++++++++++++------
mm/huge_memory.c | 54 ++++++++++-
mm/hugetlb.c | 39 +++++++-
mm/vmstat.c | 2 +
7 files changed, 322 insertions(+), 50 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 11e0086d64a4..19b3fa68a4da 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1054,6 +1054,8 @@ static inline __must_check bool try_get_page(struct page *page)
return true;
}

+__must_check bool user_page_ref_inc(struct page *page);
+
static inline void put_page(struct page *page)
{
page = compound_head(page);
@@ -1071,31 +1073,70 @@ static inline void put_page(struct page *page)
__put_page(page);
}

-/**
- * put_user_page() - release a gup-pinned page
- * @page: pointer to page to be released
+/*
+ * GUP_PIN_COUNTING_BIAS, and the associated functions that use it, overload
+ * the page's refcount so that two separate items are tracked: the original page
+ * reference count, and also a new count of how many get_user_pages() calls were
+ * made against the page. ("gup-pinned" is another term for the latter).
+ *
+ * With this scheme, get_user_pages() becomes special: such pages are marked
+ * as distinct from normal pages. As such, the new put_user_page() call (and
+ * its variants) must be used in order to release gup-pinned pages.
+ *
+ * Choice of value:
*
- * Pages that were pinned via get_user_pages*() must be released via
- * either put_user_page(), or one of the put_user_pages*() routines
- * below. This is so that eventually, pages that are pinned via
- * get_user_pages*() can be separately tracked and uniquely handled. In
- * particular, interactions with RDMA and filesystems need special
- * handling.
+ * By making GUP_PIN_COUNTING_BIAS a power of two, debugging of page reference
+ * counts with respect to get_user_pages() and put_user_page() becomes simpler,
+ * due to the fact that adding an even power of two to the page refcount has
+ * the effect of using only the upper N bits, for the code that counts up using
+ * the bias value. This means that the lower bits are left for the exclusive
+ * use of the original code that increments and decrements by one (or at least,
+ * by much smaller values than the bias value).
*
- * put_user_page() and put_page() are not interchangeable, despite this early
- * implementation that makes them look the same. put_user_page() calls must
- * be perfectly matched up with get_user_page() calls.
+ * Of course, once the lower bits overflow into the upper bits (and this is
+ * OK, because subtraction recovers the original values), then visual inspection
+ * no longer suffices to directly view the separate counts. However, for normal
+ * applications that don't have huge page reference counts, this won't be an
+ * issue.
+ *
+ * Locking: the lockless algorithm described in page_cache_get_speculative()
+ * and page_cache_gup_pin_speculative() provides safe operation for
+ * get_user_pages and page_mkclean and other calls that race to set up page
+ * table entries.
*/
-static inline void put_user_page(struct page *page)
-{
- put_page(page);
-}
+#define GUP_PIN_COUNTING_BIAS (1UL << 10)

+void put_user_page(struct page *page);
void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
bool make_dirty);
-
void put_user_pages(struct page **pages, unsigned long npages);

+/**
+ * page_dma_pinned() - report if a page is pinned for DMA.
+ *
+ * This function checks if a page has been pinned via a call to
+ * pin_user_pages*() or pin_longterm_pages*().
+ *
+ * The return value is partially fuzzy: false is not fuzzy, because it means
+ * "definitely not pinned for DMA", but true means "probably pinned for DMA, but
+ * possibly a false positive due to having at least GUP_PIN_COUNTING_BIAS worth
+ * of normal page references".
+ *
+ * False positives are OK, because: a) it's unlikely for a page to get that many
+ * refcounts, and b) all the callers of this routine are expected to be able to
+ * deal gracefully with a false positive.
+ *
+ * For more information, please see Documentation/vm/pin_user_pages.rst.
+ *
+ * @page: pointer to page to be queried.
+ * @Return: True, if it is likely that the page has been "dma-pinned".
+ * False, if the page is definitely not dma-pinned.
+ */
+static inline bool page_dma_pinned(struct page *page)
+{
+ return (page_ref_count(compound_head(page))) >= GUP_PIN_COUNTING_BIAS;
+}
+
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define SECTION_IN_PAGE_FLAGS
#endif
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index bda20282746b..0485cba38d23 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -244,6 +244,8 @@ enum node_stat_item {
NR_DIRTIED, /* page dirtyings since bootup */
NR_WRITTEN, /* page writings since bootup */
NR_KERNEL_MISC_RECLAIMABLE, /* reclaimable non-slab kernel pages */
+ NR_FOLL_PIN_REQUESTED, /* via: pin_user_page(), gup flag: FOLL_PIN */
+ NR_FOLL_PIN_RETURNED, /* pages returned via put_user_page() */
NR_VM_NODE_STAT_ITEMS
};

diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index 14d14beb1f7f..b9cbe553d1e7 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -102,6 +102,16 @@ static inline void page_ref_sub(struct page *page, int nr)
__page_ref_mod(page, -nr);
}

+static inline int page_ref_sub_return(struct page *page, int nr)
+{
+ int ret = atomic_sub_return(nr, &page->_refcount);
+
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
+ __page_ref_mod(page, -nr);
+
+ return ret;
+}
+
static inline void page_ref_inc(struct page *page)
{
atomic_inc(&page->_refcount);
diff --git a/mm/gup.c b/mm/gup.c
index ea31810da828..fc164c2ee6b5 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -44,6 +44,95 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
return head;
}

+#ifdef CONFIG_DEBUG_VM
+static inline void __update_proc_vmstat(struct page *page,
+ enum node_stat_item item, int count)
+{
+ mod_node_page_state(page_pgdat(page), item, count);
+}
+#else
+static inline void __update_proc_vmstat(struct page *page,
+ enum node_stat_item item, int count)
+{
+}
+#endif
+
+/**
+ * user_page_ref_inc() - mark a page as being used by get_user_pages(FOLL_PIN).
+ *
+ * @page: pointer to page to be marked
+ * @Return: true for success, false for failure
+ */
+__must_check bool user_page_ref_inc(struct page *page)
+{
+ page = try_get_compound_head(page, GUP_PIN_COUNTING_BIAS);
+ if (!page)
+ return false;
+
+ __update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, 1);
+ return true;
+}
+
+#ifdef CONFIG_DEV_PAGEMAP_OPS
+static bool __put_devmap_managed_user_page(struct page *page)
+{
+ bool is_devmap = page_is_devmap_managed(page);
+
+ if (is_devmap) {
+ int count = page_ref_sub_return(page, GUP_PIN_COUNTING_BIAS);
+
+ __update_proc_vmstat(page, NR_FOLL_PIN_RETURNED, 1);
+ /*
+ * devmap page refcounts are 1-based, rather than 0-based: if
+ * refcount is 1, then the page is free and the refcount is
+ * stable because nobody holds a reference on the page.
+ */
+ if (count == 1)
+ free_devmap_managed_page(page);
+ else if (!count)
+ __put_page(page);
+ }
+
+ return is_devmap;
+}
+#else
+static bool __put_devmap_managed_user_page(struct page *page)
+{
+ return false;
+}
+#endif /* CONFIG_DEV_PAGEMAP_OPS */
+
+/**
+ * put_user_page() - release a gup-pinned page
+ * @page: pointer to page to be released
+ *
+ * Pages that were pinned via get_user_pages*() must be released via
+ * either put_user_page(), or one of the put_user_pages*() routines
+ * below. This is so that eventually, pages that are pinned via
+ * get_user_pages*() can be separately tracked and uniquely handled. In
+ * particular, interactions with RDMA and filesystems need special
+ * handling.
+ */
+void put_user_page(struct page *page)
+{
+ page = compound_head(page);
+
+ /*
+ * For devmap managed pages we need to catch refcount transition from
+ * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the
+ * page is free and we need to inform the device driver through
+ * callback. See include/linux/memremap.h and HMM for details.
+ */
+ if (__put_devmap_managed_user_page(page))
+ return;
+
+ if (page_ref_sub_and_test(page, GUP_PIN_COUNTING_BIAS))
+ __put_page(page);
+
+ __update_proc_vmstat(page, NR_FOLL_PIN_RETURNED, 1);
+}
+EXPORT_SYMBOL(put_user_page);
+
/**
* put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
* @pages: array of pages to be maybe marked dirty, and definitely released.
@@ -230,10 +319,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
}

page = vm_normal_page(vma, address, pte);
- if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
+ if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) {
/*
- * Only return device mapping pages in the FOLL_GET case since
- * they are only valid while holding the pgmap reference.
+ * Only return device mapping pages in the FOLL_GET or FOLL_PIN
+ * case since they are only valid while holding the pgmap
+ * reference.
*/
*pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
if (*pgmap)
@@ -276,6 +366,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
page = ERR_PTR(-ENOMEM);
goto out;
}
+ } else if (flags & FOLL_PIN) {
+ if (unlikely(!user_page_ref_inc(page))) {
+ page = ERR_PTR(-ENOMEM);
+ goto out;
+ }
}
if (flags & FOLL_TOUCH) {
if ((flags & FOLL_WRITE) &&
@@ -537,8 +632,8 @@ static struct page *follow_page_mask(struct vm_area_struct *vma,
/* make this handle hugepd */
page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
if (!IS_ERR(page)) {
- BUG_ON(flags & FOLL_GET);
- return page;
+ WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN));
+ return NULL;
}

pgd = pgd_offset(mm, address);
@@ -1830,13 +1925,17 @@ static inline pte_t gup_get_pte(pte_t *ptep)
#endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */

static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
+ unsigned int flags,
struct page **pages)
{
while ((*nr) - nr_start) {
struct page *page = pages[--(*nr)];

ClearPageReferenced(page);
- put_page(page);
+ if (flags & FOLL_PIN)
+ put_user_page(page);
+ else
+ put_page(page);
}
}

@@ -1869,7 +1968,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,

pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
if (unlikely(!pgmap)) {
- undo_dev_pagemap(nr, nr_start, pages);
+ undo_dev_pagemap(nr, nr_start, flags, pages);
goto pte_unmap;
}
} else if (pte_special(pte))
@@ -1878,9 +1977,15 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);

- head = try_get_compound_head(page, 1);
- if (!head)
- goto pte_unmap;
+ if (flags & FOLL_PIN) {
+ head = page;
+ if (unlikely(!user_page_ref_inc(head)))
+ goto pte_unmap;
+ } else {
+ head = try_get_compound_head(page, 1);
+ if (!head)
+ goto pte_unmap;
+ }

if (unlikely(pte_val(pte) != pte_val(*ptep))) {
put_page(head);
@@ -1934,12 +2039,20 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,

pgmap = get_dev_pagemap(pfn, pgmap);
if (unlikely(!pgmap)) {
- undo_dev_pagemap(nr, nr_start, pages);
+ undo_dev_pagemap(nr, nr_start, flags, pages);
return 0;
}
SetPageReferenced(page);
pages[*nr] = page;
- get_page(page);
+
+ if (flags & FOLL_PIN) {
+ if (unlikely(!user_page_ref_inc(page))) {
+ undo_dev_pagemap(nr, nr_start, flags, pages);
+ return 0;
+ }
+ } else
+ get_page(page);
+
(*nr)++;
pfn++;
} while (addr += PAGE_SIZE, addr != end);
@@ -1961,7 +2074,7 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
return 0;

if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
- undo_dev_pagemap(nr, nr_start, pages);
+ undo_dev_pagemap(nr, nr_start, flags, pages);
return 0;
}
return 1;
@@ -1979,7 +2092,7 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
return 0;

if (unlikely(pud_val(orig) != pud_val(*pudp))) {
- undo_dev_pagemap(nr, nr_start, pages);
+ undo_dev_pagemap(nr, nr_start, flags, pages);
return 0;
}
return 1;
@@ -2063,9 +2176,16 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
refs = __record_subpages(page, addr, end, pages, *nr);

- head = try_get_compound_head(head, refs);
- if (!head)
- return 0;
+ if (flags & FOLL_PIN) {
+ head = page;
+ if (unlikely(!user_page_ref_inc(head)))
+ return 0;
+ head = page;
+ } else {
+ head = try_get_compound_head(head, refs);
+ if (!head)
+ return 0;
+ }

if (unlikely(pte_val(pte) != pte_val(*ptep))) {
put_compound_head(head, refs);
@@ -2122,9 +2242,15 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
refs = __record_subpages(page, addr, end, pages, *nr);

- head = try_get_compound_head(pmd_page(orig), refs);
- if (!head)
- return 0;
+ if (flags & FOLL_PIN) {
+ head = page;
+ if (unlikely(!user_page_ref_inc(head)))
+ return 0;
+ } else {
+ head = try_get_compound_head(pmd_page(orig), refs);
+ if (!head)
+ return 0;
+ }

if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
put_compound_head(head, refs);
@@ -2155,9 +2281,15 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
refs = __record_subpages(page, addr, end, pages, *nr);

- head = try_get_compound_head(pud_page(orig), refs);
- if (!head)
- return 0;
+ if (flags & FOLL_PIN) {
+ head = page;
+ if (unlikely(!user_page_ref_inc(head)))
+ return 0;
+ } else {
+ head = try_get_compound_head(pud_page(orig), refs);
+ if (!head)
+ return 0;
+ }

if (unlikely(pud_val(orig) != pud_val(*pudp))) {
put_compound_head(head, refs);
@@ -2183,9 +2315,15 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
refs = __record_subpages(page, addr, end, pages, *nr);

- head = try_get_compound_head(pgd_page(orig), refs);
- if (!head)
- return 0;
+ if (flags & FOLL_PIN) {
+ head = page;
+ if (unlikely(!user_page_ref_inc(head)))
+ return 0;
+ } else {
+ head = try_get_compound_head(pgd_page(orig), refs);
+ if (!head)
+ return 0;
+ }

if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
put_compound_head(head, refs);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 13cc93785006..4010c269e9e5 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -945,6 +945,11 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
*/
WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");

+ /* FOLL_GET and FOLL_PIN are mutually exclusive. */
+ if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+ (FOLL_PIN | FOLL_GET)))
+ return NULL;
+
if (flags & FOLL_WRITE && !pmd_write(*pmd))
return NULL;

@@ -960,7 +965,7 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
* device mapped pages can only be returned if the
* caller will manage the page reference count.
*/
- if (!(flags & FOLL_GET))
+ if (!(flags & (FOLL_GET | FOLL_PIN)))
return ERR_PTR(-EEXIST);

pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
@@ -968,7 +973,18 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
if (!*pgmap)
return ERR_PTR(-EFAULT);
page = pfn_to_page(pfn);
- get_page(page);
+
+ if (flags & FOLL_GET)
+ get_page(page);
+ else if (flags & FOLL_PIN) {
+ /*
+ * user_page_ref_inc() is not actually expected to fail here
+ * because we hold the pmd lock so no one can unmap the pmd and
+ * free the page that it points to.
+ */
+ if (unlikely(!user_page_ref_inc(page)))
+ page = ERR_PTR(-EFAULT);
+ }

return page;
}
@@ -1088,6 +1104,11 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
if (flags & FOLL_WRITE && !pud_write(*pud))
return NULL;

+ /* FOLL_GET and FOLL_PIN are mutually exclusive. */
+ if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+ (FOLL_PIN | FOLL_GET)))
+ return NULL;
+
if (pud_present(*pud) && pud_devmap(*pud))
/* pass */;
else
@@ -1099,8 +1120,10 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
/*
* device mapped pages can only be returned if the
* caller will manage the page reference count.
+ *
+ * At least one of FOLL_GET | FOLL_PIN must be set, so assert that here:
*/
- if (!(flags & FOLL_GET))
+ if (!(flags & (FOLL_GET | FOLL_PIN)))
return ERR_PTR(-EEXIST);

pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
@@ -1108,7 +1131,18 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
if (!*pgmap)
return ERR_PTR(-EFAULT);
page = pfn_to_page(pfn);
- get_page(page);
+
+ if (flags & FOLL_GET)
+ get_page(page);
+ else if (flags & FOLL_PIN) {
+ /*
+ * user_page_ref_inc() is not actually expected to fail here
+ * because we hold the pud lock so no one can unmap the pud and
+ * free the page that it points to.
+ */
+ if (unlikely(!user_page_ref_inc(page)))
+ page = ERR_PTR(-EFAULT);
+ }

return page;
}
@@ -1522,8 +1556,20 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
skip_mlock:
page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
+
if (flags & FOLL_GET)
get_page(page);
+ else if (flags & FOLL_PIN) {
+ /*
+ * user_page_ref_inc() is not actually expected to fail here
+ * because we hold the pmd lock so no one can unmap the pmd and
+ * free the page that it points to.
+ */
+ if (unlikely(!user_page_ref_inc(page))) {
+ WARN_ON_ONCE(1);
+ page = NULL;
+ }
+ }

out:
return page;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b45a95363a84..5ee80eea25e5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4462,7 +4462,22 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
same_page:
if (pages) {
pages[i] = mem_map_offset(page, pfn_offset);
- get_page(pages[i]);
+
+ if (flags & FOLL_GET)
+ get_page(pages[i]);
+ else if (flags & FOLL_PIN) {
+ /*
+ * user_page_ref_inc() is not actually expected
+ * to fail here because we hold the ptl.
+ */
+ if (unlikely(!user_page_ref_inc(pages[i]))) {
+ spin_unlock(ptl);
+ remainder = 0;
+ err = -ENOMEM;
+ WARN_ON_ONCE(1);
+ break;
+ }
+ }
}

if (vmas)
@@ -5022,6 +5037,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
struct page *page = NULL;
spinlock_t *ptl;
pte_t pte;
+
+ /* FOLL_GET and FOLL_PIN are mutually exclusive. */
+ if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+ (FOLL_PIN | FOLL_GET)))
+ return NULL;
+
retry:
ptl = pmd_lockptr(mm, pmd);
spin_lock(ptl);
@@ -5034,8 +5055,20 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
pte = huge_ptep_get((pte_t *)pmd);
if (pte_present(pte)) {
page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
+
if (flags & FOLL_GET)
get_page(page);
+ else if (flags & FOLL_PIN) {
+ /*
+ * user_page_ref_inc() is not actually expected to fail
+ * here because we hold the ptl.
+ */
+ if (unlikely(!user_page_ref_inc(page))) {
+ WARN_ON_ONCE(1);
+ page = NULL;
+ goto out;
+ }
+ }
} else {
if (is_hugetlb_entry_migration(pte)) {
spin_unlock(ptl);
@@ -5056,7 +5089,7 @@ struct page * __weak
follow_huge_pud(struct mm_struct *mm, unsigned long address,
pud_t *pud, int flags)
{
- if (flags & FOLL_GET)
+ if (flags & (FOLL_GET | FOLL_PIN))
return NULL;

return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
@@ -5065,7 +5098,7 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address,
struct page * __weak
follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, int flags)
{
- if (flags & FOLL_GET)
+ if (flags & (FOLL_GET | FOLL_PIN))
return NULL;

return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index a8222041bd44..fdad40ccde7b 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1167,6 +1167,8 @@ const char * const vmstat_text[] = {
"nr_dirtied",
"nr_written",
"nr_kernel_misc_reclaimable",
+ "nr_foll_pin_requested",
+ "nr_foll_pin_returned",

/* enum writeback_stat_item counters */
"nr_dirty_threshold",
--
2.24.0