linux-kernel - [PATCH 2/3] mm/page_table_check: Do WARN_ON instead of BUG

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Date:   Sun, 11 Sep 2022 09:59:22 +0000
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, akpm@...ux-foundation.org,
        corbet@....net, linux-mm@...ck.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, rick.p.edgecombe@...el.com
Subject: [PATCH 2/3] mm/page_table_check: Do WARN_ON instead of BUG_ON by default

Currently, page_table_check when detects errors panics kernel. Instead,
print a warning, and panic only when specifically requested via kernel
parameter:

	page_table_check=panic

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 mm/page_table_check.c | 53 +++++++++++++++++++++++++++++++------------
 1 file changed, 39 insertions(+), 14 deletions(-)

diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index 665ece0d55d4..881f19d0714c 100644
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -17,13 +17,37 @@ struct page_table_check {
 
 static bool __page_table_check_enabled __initdata =
 				IS_ENABLED(CONFIG_PAGE_TABLE_CHECK_ENFORCED);
+static bool __page_table_check_panic;
 
 DEFINE_STATIC_KEY_TRUE(page_table_check_disabled);
 EXPORT_SYMBOL(page_table_check_disabled);
 
+#define PAGE_TABLE_CHECK_BUG(v)							\
+	do {									\
+		bool __bug = !!(v);						\
+										\
+		if (__page_table_check_panic)					\
+			BUG_ON(__bug);						\
+		else if (WARN_ON_ONCE(__bug))					\
+			static_branch_enable(&page_table_check_disabled);	\
+	} while (false)
+
 static int __init early_page_table_check_param(char *buf)
 {
-	return strtobool(buf, &__page_table_check_enabled);
+	int rc = strtobool(buf, &__page_table_check_enabled);
+
+	if (rc) {
+		if (!strcmp(buf, "panic")) {
+			__page_table_check_enabled = true;
+			__page_table_check_panic = true;
+			rc = 0;
+		}
+	}
+
+	if (rc)
+		pr_warn("Invalid option string: '%s'\n", buf);
+
+	return rc;
 }
 
 early_param("page_table_check", early_page_table_check_param);
@@ -48,7 +72,8 @@ struct page_ext_operations page_table_check_ops = {
 
 static struct page_table_check *get_page_table_check(struct page_ext *page_ext)
 {
-	BUG_ON(!page_ext);
+	PAGE_TABLE_CHECK_BUG(!page_ext);
+
 	return (void *)(page_ext) + page_table_check_ops.offset;
 }
 
@@ -75,11 +100,11 @@ static void page_table_check_clear(struct mm_struct *mm, unsigned long addr,
 		struct page_table_check *ptc = get_page_table_check(page_ext);
 
 		if (anon) {
-			BUG_ON(atomic_read(&ptc->file_map_count));
-			BUG_ON(atomic_dec_return(&ptc->anon_map_count) < 0);
+			PAGE_TABLE_CHECK_BUG(atomic_read(&ptc->file_map_count));
+			PAGE_TABLE_CHECK_BUG(atomic_dec_return(&ptc->anon_map_count) < 0);
 		} else {
-			BUG_ON(atomic_read(&ptc->anon_map_count));
-			BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0);
+			PAGE_TABLE_CHECK_BUG(atomic_read(&ptc->anon_map_count));
+			PAGE_TABLE_CHECK_BUG(atomic_dec_return(&ptc->file_map_count) < 0);
 		}
 		page_ext = page_ext_next(page_ext);
 	}
@@ -102,7 +127,7 @@ static void page_table_check_set(struct mm_struct *mm, unsigned long addr,
 	if (!pfn_valid(pfn))
 		return;
 
-	BUG_ON(is_zero_pfn(pfn) && rw);
+	PAGE_TABLE_CHECK_BUG(!is_zero_pfn(pfn) && rw);
 
 	page = pfn_to_page(pfn);
 	page_ext = lookup_page_ext(page);
@@ -112,11 +137,11 @@ static void page_table_check_set(struct mm_struct *mm, unsigned long addr,
 		struct page_table_check *ptc = get_page_table_check(page_ext);
 
 		if (anon) {
-			BUG_ON(atomic_read(&ptc->file_map_count));
-			BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw);
+			PAGE_TABLE_CHECK_BUG(atomic_read(&ptc->file_map_count));
+			PAGE_TABLE_CHECK_BUG(atomic_inc_return(&ptc->anon_map_count) > 1 && rw);
 		} else {
-			BUG_ON(atomic_read(&ptc->anon_map_count));
-			BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0);
+			PAGE_TABLE_CHECK_BUG(atomic_read(&ptc->anon_map_count));
+			PAGE_TABLE_CHECK_BUG(atomic_inc_return(&ptc->file_map_count) < 0);
 		}
 		page_ext = page_ext_next(page_ext);
 	}
@@ -131,12 +156,12 @@ void __page_table_check_zero(struct page *page, unsigned int order)
 	struct page_ext *page_ext = lookup_page_ext(page);
 	unsigned long i;
 
-	BUG_ON(!page_ext);
+	PAGE_TABLE_CHECK_BUG(!page_ext);
 	for (i = 0; i < (1ul << order); i++) {
 		struct page_table_check *ptc = get_page_table_check(page_ext);
 
-		BUG_ON(atomic_read(&ptc->anon_map_count));
-		BUG_ON(atomic_read(&ptc->file_map_count));
+		PAGE_TABLE_CHECK_BUG(atomic_read(&ptc->anon_map_count));
+		PAGE_TABLE_CHECK_BUG(atomic_read(&ptc->file_map_count));
 		page_ext = page_ext_next(page_ext);
 	}
 }
-- 
2.37.2.789.g6183377224-goog