There's a race between fork() and hugepage migration, as a result we try to
"dereference" a swap entry as a normal pte, causing kernel panic.
The cause of the problem is that copy_hugetlb_page_range() can't handle "swap
entry" family (migration entry and hwpoisoned entry,) so let's fix it.
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v2.6.36+
---
include/linux/mm.h | 6 +++++
mm/hugetlb.c | 72 ++++++++++++++++++++++++++++++++----------------------
mm/memory.c | 5 ----
3 files changed, 49 insertions(+), 34 deletions(-)
diff --git v3.15-rc8.orig/include/linux/mm.h v3.15-rc8/include/linux/mm.h
index d6777060449f..6b4fe9ec79ba 100644
--- v3.15-rc8.orig/include/linux/mm.h
+++ v3.15-rc8/include/linux/mm.h
@@ -1924,6 +1924,12 @@ static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
return vma;
}
+static inline bool is_cow_mapping(vm_flags_t flags)
+{
+ return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
+}
+
+
#ifdef CONFIG_MMU
pgprot_t vm_get_page_prot(unsigned long vm_flags);
#else
diff --git v3.15-rc8.orig/mm/hugetlb.c v3.15-rc8/mm/hugetlb.c
index c82290b9c1fc..47ae7db288f7 100644
--- v3.15-rc8.orig/mm/hugetlb.c
+++ v3.15-rc8/mm/hugetlb.c
@@ -2377,6 +2377,31 @@ static void set_huge_ptep_writable(struct vm_area_struct *vma,
update_mmu_cache(vma, address, ptep);
}
+static int is_hugetlb_entry_migration(pte_t pte)
+{
+ swp_entry_t swp;
+
+ if (huge_pte_none(pte) || pte_present(pte))
+ return 0;
+ swp = pte_to_swp_entry(pte);
+ if (non_swap_entry(swp) && is_migration_entry(swp))
+ return 1;
+ else
+ return 0;
+}
+
+static int is_hugetlb_entry_hwpoisoned(pte_t pte)
+{
+ swp_entry_t swp;
+
+ if (huge_pte_none(pte) || pte_present(pte))
+ return 0;
+ swp = pte_to_swp_entry(pte);
+ if (non_swap_entry(swp) && is_hwpoison_entry(swp))
+ return 1;
+ else
+ return 0;
+}
int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
struct vm_area_struct *vma)
@@ -2391,7 +2416,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
unsigned long mmun_end; /* For mmu_notifiers */
int ret = 0;
- cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
+ cow = is_cow_mapping(vma->vm_flags);
mmun_start = vma->vm_start;
mmun_end = vma->vm_end;
@@ -2416,10 +2441,25 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
dst_ptl = huge_pte_lock(h, dst, dst_pte);
src_ptl = huge_pte_lockptr(h, src, src_pte);
spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
- if (!huge_pte_none(huge_ptep_get(src_pte))) {
+ entry = huge_ptep_get(src_pte);
+ if (huge_pte_none(entry)) { /* skip none entry */
+ ;
+ } else if (unlikely(is_hugetlb_entry_migration(entry) ||
+ is_hugetlb_entry_hwpoisoned(entry))) {
+ swp_entry_t swp_entry = pte_to_swp_entry(entry);
+ if (is_write_migration_entry(swp_entry) && cow) {
+ /*
+ * COW mappings require pages in both
+ * parent and child to be set to read.
+ */
+ make_migration_entry_read(&swp_entry);
+ entry = swp_entry_to_pte(swp_entry);
+ set_pte_at(src, addr, src_pte, entry);
+ }
+ set_huge_pte_at(dst, addr, dst_pte, entry);
+ } else {
if (cow)
huge_ptep_set_wrprotect(src, addr, src_pte);
- entry = huge_ptep_get(src_pte);
ptepage = pte_page(entry);
get_page(ptepage);
page_dup_rmap(ptepage);
@@ -2435,32 +2475,6 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
return ret;
}
-static int is_hugetlb_entry_migration(pte_t pte)
-{
- swp_entry_t swp;
-
- if (huge_pte_none(pte) || pte_present(pte))
- return 0;
- swp = pte_to_swp_entry(pte);
- if (non_swap_entry(swp) && is_migration_entry(swp))
- return 1;
- else
- return 0;
-}
-
-static int is_hugetlb_entry_hwpoisoned(pte_t pte)
-{
- swp_entry_t swp;
-
- if (huge_pte_none(pte) || pte_present(pte))
- return 0;
- swp = pte_to_swp_entry(pte);
- if (non_swap_entry(swp) && is_hwpoison_entry(swp))
- return 1;
- else
- return 0;
-}
-
void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
unsigned long start, unsigned long end,
struct page *ref_page)
diff --git v3.15-rc8.orig/mm/memory.c v3.15-rc8/mm/memory.c
index 037b812a9531..efc66b128976 100644
--- v3.15-rc8.orig/mm/memory.c
+++ v3.15-rc8/mm/memory.c
@@ -698,11 +698,6 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
}
-static inline bool is_cow_mapping(vm_flags_t flags)
-{
- return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
-}
-
/*
* vm_normal_page -- This function gets the "struct page" associated with a pte.
*
--
1.9.3
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