diff mbox series

[14/15] mm: fix the deadlock in finish_fault()

Message ID 20210723225041.VB3Yq9fkx%akpm@linux-foundation.org (mailing list archive)
State New
Headers show
Series [01/15] userfaultfd: do not untag user pointers | expand

Commit Message

Andrew Morton July 23, 2021, 10:50 p.m. UTC 
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(-)
diff mbox series

Patch

--- 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() */