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Subject[PATCH 35 of 66] pmd_trans_huge migrate bugcheck
Date
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From: Andrea Arcangeli <aarcange@redhat.com>

No pmd_trans_huge should ever materialize in migration ptes areas, because
we split the hugepage before migration ptes are instantiated.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
---

diff --git a/include/linux/mm.h b/include/linux/mm.h
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1475,6 +1475,7 @@ struct page *follow_page(struct vm_area_
#define FOLL_GET 0x04 /* do get_page on page */
#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */
#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
+#define FOLL_SPLIT 0x20 /* don't return transhuge pages, split them */

typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
void *data);
diff --git a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1305,6 +1305,10 @@ struct page *follow_page(struct vm_area_
goto out;
}
if (pmd_trans_huge(*pmd)) {
+ if (flags & FOLL_SPLIT) {
+ split_huge_page_pmd(mm, pmd);
+ goto split_fallthrough;
+ }
spin_lock(&mm->page_table_lock);
if (likely(pmd_trans_huge(*pmd))) {
if (unlikely(pmd_trans_splitting(*pmd))) {
@@ -1320,6 +1324,7 @@ struct page *follow_page(struct vm_area_
spin_unlock(&mm->page_table_lock);
/* fall through */
}
+split_fallthrough:
if (unlikely(pmd_bad(*pmd)))
goto no_page_table;

diff --git a/mm/migrate.c b/mm/migrate.c
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -111,6 +111,8 @@ static int remove_migration_pte(struct p
goto out;

pmd = pmd_offset(pud, addr);
+ if (pmd_trans_huge(*pmd))
+ goto out;
if (!pmd_present(*pmd))
goto out;

@@ -630,6 +632,9 @@ static int unmap_and_move(new_page_t get
/* page was freed from under us. So we are done. */
goto move_newpage;
}
+ if (unlikely(PageTransHuge(page)))
+ if (unlikely(split_huge_page(page)))
+ goto move_newpage;

/* prepare cgroup just returns 0 or -ENOMEM */
rc = -EAGAIN;
@@ -1040,7 +1045,7 @@ static int do_move_page_to_node_array(st
if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
goto set_status;

- page = follow_page(vma, pp->addr, FOLL_GET);
+ page = follow_page(vma, pp->addr, FOLL_GET|FOLL_SPLIT);

err = PTR_ERR(page);
if (IS_ERR(page))

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