Now {pmd,pte}_mkdirty() set _PAGE_DIRTY bit unconditionally, this causes
random segmentation fault after commit 0ccf7f168e17bb7e ("mm/thp: carry
over dirty bit when thp splits on pmd").
The reason is: when fork(), parent process use pmd_wrprotect() to clear
huge page's _PAGE_WRITE and _PAGE_DIRTY (for COW); then pte_mkdirty() set
_PAGE_DIRTY as well as _PAGE_MODIFIED while splitting dirty huge pages;
once _PAGE_DIRTY is set, there will be no tlb modify exception so the COW
machanism fails; and at last memory corruption occurred between parent
and child processes.
So, we should set _PAGE_DIRTY only when _PAGE_WRITE is set in {pmd,pte}_
mkdirty().
Cc: stable@xxxxxxxxxxxxxxx
Cc: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
Note: CC sparc maillist because they have similar issues.
arch/loongarch/include/asm/pgtable.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
index 946704bee599..debbe116f105 100644
--- a/arch/loongarch/include/asm/pgtable.h
+++ b/arch/loongarch/include/asm/pgtable.h
@@ -349,7 +349,9 @@ static inline pte_t pte_mkclean(pte_t pte)
static inline pte_t pte_mkdirty(pte_t pte)
{
- pte_val(pte) |= (_PAGE_DIRTY | _PAGE_MODIFIED);
+ pte_val(pte) |= _PAGE_MODIFIED;
+ if (pte_val(pte) & _PAGE_WRITE)
+ pte_val(pte) |= _PAGE_DIRTY;
return pte;
}
@@ -478,7 +480,9 @@ static inline pmd_t pmd_mkclean(pmd_t pmd)
static inline pmd_t pmd_mkdirty(pmd_t pmd)
{
- pmd_val(pmd) |= (_PAGE_DIRTY | _PAGE_MODIFIED);
+ pmd_val(pmd) |= _PAGE_MODIFIED;
+ if (pmd_val(pmd) & _PAGE_WRITE)
+ pmd_val(pmd) |= _PAGE_DIRTY;
return pmd;
}
--
2.31.1
