From: Qi Zheng zhengqi.arch@bytedance.com Subject: mm: fix the deadlock in finish_fault()

Commit 63f3655f9501 ("mm, memcg: fix reclaim deadlock with writeback") fix the following ABBA deadlock by pre-allocating the pte page table without holding the page lock.

lock_page(A) SetPageWriteback(A) unlock_page(A) lock_page(B) lock_page(B) pte_alloc_one shrink_page_list wait_on_page_writeback(A) SetPageWriteback(B) unlock_page(B)

# flush A, B to clear the writeback

Commit f9ce0be71d1f ("mm: Cleanup faultaround and finish_fault() codepaths") rework the relevant code but ignore this race. This will cause the deadlock above to appear again, so fix it.

Link: https://lkml.kernel.org/r/20210721074849.57004-1-zhengqi.arch@bytedance.com Fixes: f9ce0be71d1f ("mm: Cleanup faultaround and finish_fault() codepaths") Signed-off-by: Qi Zheng zhengqi.arch@bytedance.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@kernel.org Cc: Vladimir Davydov vdavydov.dev@gmail.com Cc: Muchun Song songmuchun@bytedance.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memory.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/mm/memory.c~mm-fix-the-deadlock-in-finish_fault +++ a/mm/memory.c @@ -4026,8 +4026,17 @@ vm_fault_t finish_fault(struct vm_fault return ret; }

- if (unlikely(pte_alloc(vma->vm_mm, vmf->pmd))) + if (vmf->prealloc_pte) { + vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd); + if (likely(pmd_none(*vmf->pmd))) { + mm_inc_nr_ptes(vma->vm_mm); + pmd_populate(vma->vm_mm, vmf->pmd, vmf->prealloc_pte); + vmf->prealloc_pte = NULL; + } + spin_unlock(vmf->ptl); + } else if (unlikely(pte_alloc(vma->vm_mm, vmf->pmd))) { return VM_FAULT_OOM; + } }

/* See comment in handle_pte_fault() */ _