thp: avoid race on multiple parallel page faults to the same page
pmd value is stable only with mm->page_table_lock taken. After taking
the lock we need to check that nobody modified the pmd before changing it.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Reviewed-by: Bob Liu <lliubbo@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 72835ce..827d9c8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -769,17 +769,20 @@
}
#endif
-static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
+static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
unsigned long zero_pfn)
{
pmd_t entry;
+ if (!pmd_none(*pmd))
+ return false;
entry = pfn_pmd(zero_pfn, vma->vm_page_prot);
entry = pmd_wrprotect(entry);
entry = pmd_mkhuge(entry);
set_pmd_at(mm, haddr, pmd, entry);
pgtable_trans_huge_deposit(mm, pgtable);
mm->nr_ptes++;
+ return true;
}
int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
@@ -799,6 +802,7 @@
transparent_hugepage_use_zero_page()) {
pgtable_t pgtable;
unsigned long zero_pfn;
+ bool set;
pgtable = pte_alloc_one(mm, haddr);
if (unlikely(!pgtable))
return VM_FAULT_OOM;
@@ -809,9 +813,13 @@
goto out;
}
spin_lock(&mm->page_table_lock);
- set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
+ set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
zero_pfn);
spin_unlock(&mm->page_table_lock);
+ if (!set) {
+ pte_free(mm, pgtable);
+ put_huge_zero_page();
+ }
return 0;
}
page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
@@ -885,14 +893,16 @@
*/
if (is_huge_zero_pmd(pmd)) {
unsigned long zero_pfn;
+ bool set;
/*
* get_huge_zero_page() will never allocate a new page here,
* since we already have a zero page to copy. It just takes a
* reference.
*/
zero_pfn = get_huge_zero_page();
- set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
+ set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
zero_pfn);
+ BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
ret = 0;
goto out_unlock;
}
@@ -949,7 +959,7 @@
static int do_huge_pmd_wp_zero_page_fallback(struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long address,
- pmd_t *pmd, unsigned long haddr)
+ pmd_t *pmd, pmd_t orig_pmd, unsigned long haddr)
{
pgtable_t pgtable;
pmd_t _pmd;
@@ -978,6 +988,9 @@
mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
spin_lock(&mm->page_table_lock);
+ if (unlikely(!pmd_same(*pmd, orig_pmd)))
+ goto out_free_page;
+
pmdp_clear_flush(vma, haddr, pmd);
/* leave pmd empty until pte is filled */
@@ -1010,6 +1023,12 @@
ret |= VM_FAULT_WRITE;
out:
return ret;
+out_free_page:
+ spin_unlock(&mm->page_table_lock);
+ mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+ mem_cgroup_uncharge_page(page);
+ put_page(page);
+ goto out;
}
static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
@@ -1156,7 +1175,7 @@
count_vm_event(THP_FAULT_FALLBACK);
if (is_huge_zero_pmd(orig_pmd)) {
ret = do_huge_pmd_wp_zero_page_fallback(mm, vma,
- address, pmd, haddr);
+ address, pmd, orig_pmd, haddr);
} else {
ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
pmd, orig_pmd, page, haddr);