mm: kfence: fix PG_slab and memcg_data clearing

It does not reset PG_slab and memcg_data when KFENCE fails to initialize
kfence pool at runtime.  It is reporting a "Bad page state" message when
kfence pool is freed to buddy.  The checking of whether it is a compound
head page seems unnecessary since we already guarantee this when
allocating kfence pool.   Remove the check to simplify the code.

Link: https://lkml.kernel.org/r/20230320030059.20189-1-songmuchun@bytedance.com
Fixes: 0ce20dd8 ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: SeongJae Park <sjpark@amazon.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/kfence/core.c

@@ -561,10 +561,6 @@ static unsigned long kfence_init_pool(void)
 		if (!i || (i % 2))
 			continue;
 
-		/* Verify we do not have a compound head page. */
-		if (WARN_ON(compound_head(&pages[i]) != &pages[i]))
-			return addr;
-
 		__folio_set_slab(slab_folio(slab));
 #ifdef CONFIG_MEMCG
 		slab->memcg_data = (unsigned long)&kfence_metadata[i / 2 - 1].objcg |
@@ -597,12 +593,26 @@ static unsigned long kfence_init_pool(void)
 
 		/* Protect the right redzone. */
 		if (unlikely(!kfence_protect(addr + PAGE_SIZE)))
-			return addr;
+			goto reset_slab;
 
 		addr += 2 * PAGE_SIZE;
 	}
 
 	return 0;
+
+reset_slab:
+	for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
+		struct slab *slab = page_slab(&pages[i]);
+
+		if (!i || (i % 2))
+			continue;
+#ifdef CONFIG_MEMCG
+		slab->memcg_data = 0;
+#endif
+		__folio_clear_slab(slab_folio(slab));
+	}
+
+	return addr;
 }
 
 static bool __init kfence_init_pool_early(void)
@@ -632,16 +642,6 @@ static bool __init kfence_init_pool_early(void)
 	 * fails for the first page, and therefore expect addr==__kfence_pool in
 	 * most failure cases.
 	 */
-	for (char *p = (char *)addr; p < __kfence_pool + KFENCE_POOL_SIZE; p += PAGE_SIZE) {
-		struct slab *slab = virt_to_slab(p);
-
-		if (!slab)
-			continue;
-#ifdef CONFIG_MEMCG
-		slab->memcg_data = 0;
-#endif
-		__folio_clear_slab(slab_folio(slab));
-	}
 	memblock_free_late(__pa(addr), KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool));
 	__kfence_pool = NULL;
 	return false;