mm/page_vma_mapped: pte_offset_map_nolock() not pte_lockptr()

map_pte() use pte_offset_map_nolock(), to make sure of the ptl belonging
to pte, even if pmd entry is then changed racily: page_vma_mapped_walk()
use that instead of getting pte_lockptr() later, or restart if map_pte()
found no page table.

Link: https://lkml.kernel.org/r/cba186e0-5ed7-e81b-6cd-dade4c33c248@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 947dc74..2af7342 100644 (file)
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -13,16 +13,28 @@ static inline bool not_found(struct page_vma_mapped_walk *pvmw)
        return false;
 }
 
-static bool map_pte(struct page_vma_mapped_walk *pvmw)
+static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp)
 {
        if (pvmw->flags & PVMW_SYNC) {
                /* Use the stricter lookup */
                pvmw->pte = pte_offset_map_lock(pvmw->vma->vm_mm, pvmw->pmd,
                                                pvmw->address, &pvmw->ptl);
-               return true;
+               *ptlp = pvmw->ptl;
+               return !!pvmw->pte;
        }
 
-       pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
+       /*
+        * It is important to return the ptl corresponding to pte,
+        * in case *pvmw->pmd changes underneath us; so we need to
+        * return it even when choosing not to lock, in case caller
+        * proceeds to loop over next ptes, and finds a match later.
+        * Though, in most cases, page lock already protects this.
+        */
+       pvmw->pte = pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd,
+                                         pvmw->address, ptlp);
+       if (!pvmw->pte)
+               return false;
+
        if (pvmw->flags & PVMW_MIGRATION) {
                if (!is_swap_pte(*pvmw->pte))
                        return false;
@@ -51,7 +63,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw)
        } else if (!pte_present(*pvmw->pte)) {
                return false;
        }
-       pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
+       pvmw->ptl = *ptlp;
        spin_lock(pvmw->ptl);
        return true;
 }
@@ -156,6 +168,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
        struct vm_area_struct *vma = pvmw->vma;
        struct mm_struct *mm = vma->vm_mm;
        unsigned long end;
+       spinlock_t *ptl;
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
@@ -257,8 +270,11 @@ restart:
                        step_forward(pvmw, PMD_SIZE);
                        continue;
                }
-               if (!map_pte(pvmw))
+               if (!map_pte(pvmw, &ptl)) {
+                       if (!pvmw->pte)
+                               goto restart;
                        goto next_pte;
+               }
 this_pte:
                if (check_pte(pvmw))
                        return true;
@@ -281,7 +297,7 @@ next_pte:
                } while (pte_none(*pvmw->pte));
 
                if (!pvmw->ptl) {
-                       pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
+                       pvmw->ptl = ptl;
                        spin_lock(pvmw->ptl);
                }
                goto this_pte;