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") 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: 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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index 747a01d495f2c5cd0ff71e0910925a3374af316d..25fc46e872142a11692e3b44402cab89ca644fb3 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4026,8 +4026,17 @@ 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() */