mm/memory: handle_pte_fault() use pte_offset_map_nolock()

handle_pte_fault() use pte_offset_map_nolock() to get the vmf.ptl which
corresponds to vmf.pte, instead of pte_lockptr() being used later, when
there's a chance that the pmd entry might have changed, perhaps to none,
or to a huge pmd, with no split ptlock in its struct page.

Remove its pmd_devmap_trans_unstable() call: pte_offset_map_nolock() will
handle that case by failing.  Update the "morph" comment above, looking
forward to when shmem or file collapse to THP may not take mmap_lock for
write (or not at all).

do_numa_page() use the vmf->ptl from handle_pte_fault() at first, but
refresh it when refreshing vmf->pte.

do_swap_page()'s pte_unmap_same() (the thing that takes ptl to verify a
two-part PAE orig_pte) use the vmf->ptl from handle_pte_fault() too; but
do_swap_page() is also used by anon THP's __collapse_huge_page_swapin(),
so adjust that to set vmf->ptl by pte_offset_map_nolock().

Link: https://lkml.kernel.org/r/c1107654-3929-60ac-223e-6877cbb86065@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>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 04c22b5309d7..d1951ed572f8 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1003,6 +1003,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
 	unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE);
 	int result;
 	pte_t *pte = NULL;
+	spinlock_t *ptl;
 
 	for (address = haddr; address < end; address += PAGE_SIZE) {
 		struct vm_fault vmf = {
@@ -1014,7 +1015,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
 		};
 
 		if (!pte++) {
-			pte = pte_offset_map(pmd, address);
+			pte = pte_offset_map_nolock(mm, pmd, address, &ptl);
 			if (!pte) {
 				mmap_read_unlock(mm);
 				result = SCAN_PMD_NULL;
@@ -1022,11 +1023,12 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
 			}
 		}
 
-		vmf.orig_pte = *pte;
+		vmf.orig_pte = ptep_get_lockless(pte);
 		if (!is_swap_pte(vmf.orig_pte))
 			continue;
 
 		vmf.pte = pte;
+		vmf.ptl = ptl;
 		ret = do_swap_page(&vmf);
 		/* Which unmaps pte (after perhaps re-checking the entry) */
 		pte = NULL;