perf/core: allow pte_offset_map() to fail

In rare transient cases, not yet made possible, pte_offset_map() and
pte_offet_map_lock() may not find a page table: handle appropriately.

[hughd@google.com: __wp_page_copy_user(): don't call update_mmu_tlb() with NULL]
  Link: https://lkml.kernel.org/r/1a4db221-7872-3594-57ce-42369945ec8d@google.com
Link: https://lkml.kernel.org/r/a194441b-63f3-adb6-5964-7ca3171ae7c2@google.comSigned-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>

kernel/events/core.c

@@ -7490,6 +7490,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr)
 		return pud_leaf_size(pud);
 
 	pmdp = pmd_offset_lockless(pudp, pud, addr);
+again:
 	pmd = pmdp_get_lockless(pmdp);
 	if (!pmd_present(pmd))
 		return 0;
@@ -7498,6 +7499,9 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr)
 		return pmd_leaf_size(pmd);
 
 	ptep = pte_offset_map(&pmd, addr);
+	if (!ptep)
+		goto again;
+
 	pte = ptep_get_lockless(ptep);
 	if (pte_present(pte))
 		size = pte_leaf_size(pte);

mm/memory.c

@@ -2843,7 +2843,8 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
 			 * Other thread has already handled the fault
 			 * and update local tlb only
 			 */
-			update_mmu_tlb(vma, addr, vmf->pte);
+			if (vmf->pte)
+				update_mmu_tlb(vma, addr, vmf->pte);
 			ret = -EAGAIN;
 			goto pte_unlock;
 		}
@@ -2867,7 +2868,8 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
 		vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
 		if (unlikely(!vmf->pte || !pte_same(*vmf->pte, vmf->orig_pte))) {
 			/* The PTE changed under us, update local tlb */
-			update_mmu_tlb(vma, addr, vmf->pte);
+			if (vmf->pte)
+				update_mmu_tlb(vma, addr, vmf->pte);
 			ret = -EAGAIN;
 			goto pte_unlock;
 		}