9 files changed, 25 insertions, 55 deletions

diff --git a/drivers/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c
index 8184451b57c0..422b7d84f686 100644
--- a/drivers/block/aoe/aoecmd.c
+++ b/drivers/block/aoe/aoecmd.c
@@ -874,7 +874,7 @@ bio_pageinc(struct bio *bio)
                 /* Non-zero page count for non-head members of
                  * compound pages is no longer allowed by the kernel.
                  */
-                page = compound_trans_head(bv.bv_page);
+                page = compound_head(bv.bv_page);
                 atomic_inc(&page->_count);
         }
 }
@@ -887,7 +887,7 @@ bio_pagedec(struct bio *bio)
         struct bvec_iter iter;
 
         bio_for_each_segment(bv, bio, iter) {
-                page = compound_trans_head(bv.bv_page);
+                page = compound_head(bv.bv_page);
                 atomic_dec(&page->_count);
         }
 }
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 4fb7a8f83c8a..54af4e933695 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -186,12 +186,12 @@ static bool is_invalid_reserved_pfn(unsigned long pfn)
         if (pfn_valid(pfn)) {
                 bool reserved;
                 struct page *tail = pfn_to_page(pfn);
-                struct page *head = compound_trans_head(tail);
+                struct page *head = compound_head(tail);
                 reserved = !!(PageReserved(head));
                 if (head != tail) {
                         /*
                          * "head" is not a dangling pointer
-                         * (compound_trans_head takes care of that)
+                         * (compound_head takes care of that)
                          * but the hugepage may have been split
                          * from under us (and we may not hold a
                          * reference count on the head page so it can
diff --git a/fs/proc/page.c b/fs/proc/page.c
index 02174a610315..e647c55275d9 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -121,9 +121,8 @@ u64 stable_page_flags(struct page *page)
          * just checks PG_head/PG_tail, so we need to check PageLRU/PageAnon
          * to make sure a given page is a thp, not a non-huge compound page.
          */
-        else if (PageTransCompound(page) &&
-                 (PageLRU(compound_trans_head(page)) ||
-                  PageAnon(compound_trans_head(page))))
+        else if (PageTransCompound(page) && (PageLRU(compound_head(page)) ||
+                                             PageAnon(compound_head(page))))
                 u |= 1 << KPF_THP;
 
         /*
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index db512014e061..b826239bdce0 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -157,46 +157,6 @@ static inline int hpage_nr_pages(struct page *page)
                 return HPAGE_PMD_NR;
         return 1;
 }
-/*
- * compound_trans_head() should be used instead of compound_head(),
- * whenever the "page" passed as parameter could be the tail of a
- * transparent hugepage that could be undergoing a
- * __split_huge_page_refcount(). The page structure layout often
- * changes across releases and it makes extensive use of unions. So if
- * the page structure layout will change in a way that
- * page->first_page gets clobbered by __split_huge_page_refcount, the
- * implementation making use of smp_rmb() will be required.
- *
- * Currently we define compound_trans_head as compound_head, because
- * page->private is in the same union with page->first_page, and
- * page->private isn't clobbered. However this also means we're
- * currently leaving dirt into the page->private field of anonymous
- * pages resulting from a THP split, instead of setting page->private
- * to zero like for every other page that has PG_private not set. But
- * anonymous pages don't use page->private so this is not a problem.
- */
-#if 0
-/* This will be needed if page->private will be clobbered in split_huge_page */
-static inline struct page *compound_trans_head(struct page *page)
-{
-        if (PageTail(page)) {
-                struct page *head;
-                head = page->first_page;
-                smp_rmb();
-                /*
-                 * head may be a dangling pointer.
-                 * __split_huge_page_refcount clears PageTail before
-                 * overwriting first_page, so if PageTail is still
-                 * there it means the head pointer isn't dangling.
-                 */
-                if (PageTail(page))
-                        return head;
-        }
-        return page;
-}
-#else
-#define compound_trans_head(page) compound_head(page)
-#endif
 
 extern int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                                 unsigned long addr, pmd_t pmd, pmd_t *pmdp);
@@ -226,7 +186,6 @@ static inline int split_huge_page(struct page *page)
         do { } while (0)
 #define split_huge_page_pmd_mm(__mm, __address, __pmd)  \
         do { } while (0)
-#define compound_trans_head(page) compound_head(page)
 static inline int hugepage_madvise(struct vm_area_struct *vma,
                                    unsigned long *vm_flags, int advice)
 {
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f28f46eade6a..03ab3e58f511 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -399,8 +399,18 @@ static inline void compound_unlock_irqrestore(struct page *page,
 
 static inline struct page *compound_head(struct page *page)
 {
-        if (unlikely(PageTail(page)))
-                return page->first_page;
+        if (unlikely(PageTail(page))) {
+                struct page *head = page->first_page;
+
+                /*
+                 * page->first_page may be a dangling pointer to an old
+                 * compound page, so recheck that it is still a tail
+                 * page before returning.
+                 */
+                smp_rmb();
+                if (likely(PageTail(page)))
+                        return head;
+        }
         return page;
 }
 
diff --git a/mm/ksm.c b/mm/ksm.c
index aa4c7c7250c1..68710e80994a 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -444,7 +444,7 @@ static void break_cow(struct rmap_item *rmap_item)
 static struct page *page_trans_compound_anon(struct page *page)
 {
         if (PageTransCompound(page)) {
-                struct page *head = compound_trans_head(page);
+                struct page *head = compound_head(page);
                 /*
                  * head may actually be splitted and freed from under
                  * us but it's ok here.
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 2f2f34a4e77d..90002ea43638 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1651,7 +1651,7 @@ int soft_offline_page(struct page *page, int flags)
 {
         int ret;
         unsigned long pfn = page_to_pfn(page);
-        struct page *hpage = compound_trans_head(page);
+        struct page *hpage = compound_head(page);
 
         if (PageHWPoison(page)) {
                 pr_info("soft offline: %#lx page already poisoned\n", pfn);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e3758a09a009..3d1bf889465a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -369,9 +369,11 @@ void prep_compound_page(struct page *page, unsigned long order)
         __SetPageHead(page);
         for (i = 1; i < nr_pages; i++) {
                 struct page *p = page + i;
-                __SetPageTail(p);
                 set_page_count(p, 0);
                 p->first_page = page;
+                /* Make sure p->first_page is always valid for PageTail() */
+                smp_wmb();
+                __SetPageTail(p);
         }
 }
 
diff --git a/mm/swap.c b/mm/swap.c
index b31ba67d440a..0092097b3f4c 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -98,7 +98,7 @@ static void put_compound_page(struct page *page)
         }
 
         /* __split_huge_page_refcount can run under us */
-        page_head = compound_trans_head(page);
+        page_head = compound_head(page);
 
         /*
          * THP can not break up slab pages so avoid taking
@@ -253,7 +253,7 @@ bool __get_page_tail(struct page *page)
          */
         unsigned long flags;
         bool got;
-        struct page *page_head = compound_trans_head(page);
+        struct page *page_head = compound_head(page);
 
         /* Ref to put_compound_page() comment. */
         if (!__compound_tail_refcounted(page_head)) {