From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754304AbcJNPVS (ORCPT ); Fri, 14 Oct 2016 11:21:18 -0400 Received: from mail-wm0-f46.google.com ([74.125.82.46]:37865 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752578AbcJNPVC (ORCPT ); Fri, 14 Oct 2016 11:21:02 -0400 From: Dmitry Vyukov To: aryabinin@virtuozzo.com, akpm@linux-foundation.org, glider@google.com, iamjoonsoo.kim@lge.com Cc: Dmitry Vyukov , kasan-dev@googlegroups.com, sploving1@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] lib: bump stackdepot capacity from 16MB to 128MB Date: Fri, 14 Oct 2016 17:20:16 +0200 Message-Id: <1476458416-122131-1-git-send-email-dvyukov@google.com> X-Mailer: git-send-email 2.8.0.rc3.226.g39d4020 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org KASAN uses stackdepot to memorize stacks for all kmalloc/kfree calls. Current stackdepot capacity is 16MB (1024 top level entries x 4 pages on second level). Size of each stack is (num_frames + 3) * sizeof(long). Which gives us ~84K stacks. This capacity was chosen empirically and it is enough to run kernel normally. However, when lots of configs are enabled and a fuzzer tries to maximize code coverage, it easily hits the limit within tens of minutes. I've tested for long a time with number of top level entries bumped 4x (4096). And I think I've seen overflow only once. But I don't have all configs enabled and code coverage has not reached maximum yet. So bump it 8x to 8192. Since we have two-level table, memory cost of this is very moderate -- currently the top-level table is 8KB, with this patch it is 64KB, which is negligible under KASAN. Here is some approx math. 128MB allows us to memorize ~670K stacks (assuming stack is ~200b). I've grepped kernel for kmalloc|kfree|kmem_cache_alloc|kmem_cache_free| kzalloc|kstrdup|kstrndup|kmemdup and it gives ~60K matches. Most of alloc/free call sites are reachable with only one stack. But some utility functions can have large fanout. Assuming average fanout is 5x, total number of alloc/free stacks is ~300K. Signed-off-by: Dmitry Vyukov Cc: kasan-dev@googlegroups.com Cc: Andrey Ryabinin Cc: Alexander Potapenko Cc: Andrew Morton Cc: Joonsoo Kim Cc: sploving1@gmail.com Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org --- lib/stackdepot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 60f77f1..4d830e2 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -50,7 +50,7 @@ STACK_ALLOC_ALIGN) #define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \ STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS) -#define STACK_ALLOC_SLABS_CAP 1024 +#define STACK_ALLOC_SLABS_CAP 8192 #define STACK_ALLOC_MAX_SLABS \ (((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \ (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP) -- 2.8.0.rc3.226.g39d4020