On Fri, Apr 04, 2014 at 03:37:20PM -0400, Sasha Levin wrote:
> And another ping exactly a year later :)
I think we could "fix" this false positive with the patch below
(untested), but it's ugly and doesn't add much value.
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6ac89e9f82ef..65ac113037e4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1053,6 +1053,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct
vm_area_struct *vma,
unsigned long haddr;
unsigned long mmun_start; /* For mmu_notifiers */
unsigned long mmun_end; /* For mmu_notifiers */
+ pmd_t entry;
ptl = pmd_lockptr(mm, pmd);
VM_BUG_ON(!vma->anon_vma);
@@ -1115,42 +1116,45 @@ alloc:
count_vm_event(THP_FAULT_ALLOC);
+ mmun_start = haddr;
+ mmun_end = haddr + HPAGE_PMD_SIZE;
+ mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+
+ if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
+ spin_lock(ptl);
+ if (unlikely(!pmd_same(*pmd, orig_pmd)))
+ goto out_race;
+ }
+
if (!page)
clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
else
copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
__SetPageUptodate(new_page);
- mmun_start = haddr;
- mmun_end = haddr + HPAGE_PMD_SIZE;
- mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
-
- spin_lock(ptl);
+ if (!IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
+ spin_lock(ptl);
+ if (unlikely(!pmd_same(*pmd, orig_pmd)))
+ goto out_race;
+ }
if (page)
put_page(page);
- if (unlikely(!pmd_same(*pmd, orig_pmd))) {
- spin_unlock(ptl);
- mem_cgroup_uncharge_page(new_page);
- put_page(new_page);
- goto out_mn;
+
+ entry = mk_huge_pmd(new_page, vma->vm_page_prot);
+ entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+ pmdp_clear_flush(vma, haddr, pmd);
+ page_add_new_anon_rmap(new_page, vma, haddr);
+ set_pmd_at(mm, haddr, pmd, entry);
+ update_mmu_cache_pmd(vma, address, pmd);
+ if (!page) {
+ add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
+ put_huge_zero_page();
} else {
- pmd_t entry;
- entry = mk_huge_pmd(new_page, vma->vm_page_prot);
- entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
- pmdp_clear_flush(vma, haddr, pmd);
- page_add_new_anon_rmap(new_page, vma, haddr);
- set_pmd_at(mm, haddr, pmd, entry);
- update_mmu_cache_pmd(vma, address, pmd);
- if (!page) {
- add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
- put_huge_zero_page();
- } else {
- VM_BUG_ON_PAGE(!PageHead(page), page);
- page_remove_rmap(page);
- put_page(page);
- }
- ret |= VM_FAULT_WRITE;
+ VM_BUG_ON_PAGE(!PageHead(page), page);
+ page_remove_rmap(page);
+ put_page(page);
}
+ ret |= VM_FAULT_WRITE;
spin_unlock(ptl);
out_mn:
mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
@@ -1159,6 +1163,13 @@ out:
out_unlock:
spin_unlock(ptl);
return ret;
+out_race:
+ spin_unlock(ptl);
+ if (page)
+ put_page(page);
+ mem_cgroup_uncharge_page(new_page);
+ put_page(new_page);
+ goto out_mn;
}
struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
--
Kirill A. Shutemov
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