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Date:   Thu, 8 Jun 2023 18:27:52 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
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        Mike Rapoport <rppt@kernel.org>,
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Subject: [PATCH v2 16/32] mm/debug_vm_pgtable,page_table_check: warn pte map
 fails
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Failures here would be surprising: pte_advanced_tests() and
pte_clear_tests() and __page_table_check_pte_clear_range() each
issue a warning if pte_offset_map() or pte_offset_map_lock() fails.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
 mm/debug_vm_pgtable.c | 9 ++++++++-
 mm/page_table_check.c | 2 ++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index c54177aabebd..ee119e33fef1 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -138,6 +138,9 @@ static void __init pte_advanced_tests(struct pgtable_debug_args *args)
 		return;
 
 	pr_debug("Validating PTE advanced\n");
+	if (WARN_ON(!args->ptep))
+		return;
+
 	pte = pfn_pte(args->pte_pfn, args->page_prot);
 	set_pte_at(args->mm, args->vaddr, args->ptep, pte);
 	flush_dcache_page(page);
@@ -619,6 +622,9 @@ static void __init pte_clear_tests(struct pgtable_debug_args *args)
 	 * the unexpected overhead of cache flushing is acceptable.
 	 */
 	pr_debug("Validating PTE clear\n");
+	if (WARN_ON(!args->ptep))
+		return;
+
 #ifndef CONFIG_RISCV
 	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
 #endif
@@ -1377,7 +1383,8 @@ static int __init debug_vm_pgtable(void)
 	args.ptep = pte_offset_map_lock(args.mm, args.pmdp, args.vaddr, &ptl);
 	pte_clear_tests(&args);
 	pte_advanced_tests(&args);
-	pte_unmap_unlock(args.ptep, ptl);
+	if (args.ptep)
+		pte_unmap_unlock(args.ptep, ptl);
 
 	ptl = pmd_lock(args.mm, args.pmdp);
 	pmd_clear_tests(&args);
diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index f2baf97d5f38..b743a2f6bce0 100644
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -246,6 +246,8 @@ void __page_table_check_pte_clear_range(struct mm_struct *mm,
 		pte_t *ptep = pte_offset_map(&pmd, addr);
 		unsigned long i;
 
+		if (WARN_ON(!ptep))
+			return;
 		for (i = 0; i < PTRS_PER_PTE; i++) {
 			__page_table_check_pte_clear(mm, addr, *ptep);
 			addr += PAGE_SIZE;
-- 
2.35.3