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H A D | pgtable.h | bf2f34a5 Mon Nov 21 05:02:57 CST 2022 Huacai Chen <chenhuacai@loongson.cn> LoongArch: Set _PAGE_DIRTY only if _PAGE_WRITE is set in {pmd,pte}_mkdirty()
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@vger.kernel.org Cc: Peter Xu <peterx@redhat.com> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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