mm/mglru: allow pte_offset_map_nolock() to fail

MGLRU's walk_pte_range() use the safer pte_offset_map_nolock(), rather
than pte_lockptr(), to get the ptl for its trylock.  Just return false and
move on to next extent if it fails, like when the trylock fails.  Remove
the VM_WARN_ON_ONCE(pmd_leaf) since that will happen, rarely.

Link: https://lkml.kernel.org/r/51ece73e-7398-2e4a-2384-56708c87844f@google.comSigned-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Yu Zhao <yuzhao@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: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -4024,15 +4024,15 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 	struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec);
 	int old_gen, new_gen = lru_gen_from_seq(walk->max_seq);
 
-	VM_WARN_ON_ONCE(pmd_leaf(*pmd));
-
-	ptl = pte_lockptr(args->mm, pmd);
-	if (!spin_trylock(ptl))
+	pte = pte_offset_map_nolock(args->mm, pmd, start & PMD_MASK, &ptl);
+	if (!pte)
 		return false;
+	if (!spin_trylock(ptl)) {
+		pte_unmap(pte);
+		return false;
+	}
 
 	arch_enter_lazy_mmu_mode();
-
-	pte = pte_offset_map(pmd, start & PMD_MASK);
 restart:
 	for (i = pte_index(start), addr = start; addr != end; i++, addr += PAGE_SIZE) {
 		unsigned long pfn;
@@ -4073,10 +4073,8 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 	if (i < PTRS_PER_PTE && get_next_vma(PMD_MASK, PAGE_SIZE, args, &start, &end))
 		goto restart;
 
-	pte_unmap(pte);
-
 	arch_leave_lazy_mmu_mode();
-	spin_unlock(ptl);
+	pte_unmap_unlock(pte, ptl);
 
 	return suitable_to_scan(total, young);
 }