Commit e4dc3489 authored Jul 23, 2021 by Qi Zheng Committed by Linus Torvalds Jul 23, 2021

mm: fix the deadlock in finish_fault()

Commit 63f3655f ("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 f9ce0be7 ("mm: Cleanup faultaround and finish_fault()
codepaths") reworked the relevant code but ignored 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: f9ce0be7 ("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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent e904c2cc

mm/memory.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -4026,9 +4026,18 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
		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() */
		if (pmd_devmap_trans_unstable(vmf->pmd))