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[23.128.96.18]) by mx.google.com with ESMTP id f12si1795676edx.227.2021.05.12.19.55.37; Wed, 12 May 2021 19:56:01 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@linux-foundation.org header.s=korg header.b=HHlAXi1s; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230405AbhEMCxk (ORCPT + 99 others); Wed, 12 May 2021 22:53:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:52246 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230385AbhEMCxh (ORCPT ); Wed, 12 May 2021 22:53:37 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 3E13061417; Thu, 13 May 2021 02:52:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1620874348; bh=SLbN/DBHHqmewlE8uQW14WObooHOO9whfbtyrGVG5b4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=HHlAXi1swYbztV+Xl0lXmdlm3Z62D/XY9oFpu3fdX9TfOekyShsSj+vQncgpZW7KI V5ZGTTo5f+r8od0SCbHo+X9celx0dnl2PvXHYQlmLXs57CaHKYzEeJQnGtu53dn8us HSJMlHfMNx0AkWyONanHd9JPnE3WKYCBojTArl0Y= Date: Wed, 12 May 2021 19:52:27 -0700 From: Andrew Morton To: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: vbabka@suse.cz, iamjoonsoo.kim@lge.com, rientjes@google.com, penberg@kernel.org, cl@linux.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Marco Elver Subject: Re: [PATCH v3] mm, slub: change run-time assertion in kmalloc_index() to compile-time Message-Id: <20210512195227.245000695c9014242e9a00e5@linux-foundation.org> In-Reply-To: <20210511173448.GA54466@hyeyoo> References: <20210511173448.GA54466@hyeyoo> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 12 May 2021 02:34:48 +0900 Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote: > currently when size is not supported by kmalloc_index, compiler will > generate a run-time BUG() while compile-time error is also possible, > and better. so changed BUG to BUILD_BUG_ON_MSG to make compile-time > check possible. > > also removed code that allocates more than 32MB because current > implementation supports only up to 32MB. > This explodes in mysterious ways. The patch as I have it is appended, for reference. gcc-10.3.0 allmodconfig. mm/kfence/kfence_test.c: In function 'test_free_bulk': mm/kfence/kfence_test.c:519:16: warning: unused variable 'size' [-Wunused-variable] 519 | const size_t size = setup_test_cache(test, 8 + prandom_u32_max(300), 0, | ^~~~ In file included from : In function 'kmalloc_index', inlined from 'test_alloc' at mm/kfence/kfence_test.c:270:82: ././include/linux/compiler_types.h:328:38: error: call to '__compiletime_assert_922' declared with attribute error: unexpected size in kmalloc_index() 328 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^ ././include/linux/compiler_types.h:309:4: note: in definition of macro '__compiletime_assert' 309 | prefix ## suffix(); \ | ^~~~~~ ././include/linux/compiler_types.h:328:2: note: in expansion of macro '_compiletime_assert' 328 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^~~~~~~~~~~~~~~~~~~ ./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert' 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) | ^~~~~~~~~~~~~~~~~~ ./include/linux/slab.h:389:2: note: in expansion of macro 'BUILD_BUG_ON_MSG' 389 | BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()"); | ^~~~~~~~~~~~~~~~ make[2]: *** [mm/kfence/kfence_test.o] Error 1 make[1]: *** [mm/kfence] Error 2 make: *** [mm] Error 2 This patch suppresses the error: --- a/mm/kfence/kfence_test.c~a +++ a/mm/kfence/kfence_test.c @@ -318,13 +318,13 @@ static void test_out_of_bounds_read(stru /* Test both sides. */ - buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_LEFT); + buf = test_alloc(test, 32, GFP_KERNEL, ALLOCATE_LEFT); expect.addr = buf - 1; READ_ONCE(*expect.addr); KUNIT_EXPECT_TRUE(test, report_matches(&expect)); test_free(buf); - buf = test_alloc(test, size, GFP_KERNEL, ALLOCATE_RIGHT); + buf = test_alloc(test, 32, GFP_KERNEL, ALLOCATE_RIGHT); expect.addr = buf + size; READ_ONCE(*expect.addr); KUNIT_EXPECT_TRUE(test, report_matches(&expect)); @@ -519,11 +519,11 @@ static void test_free_bulk(struct kunit const size_t size = setup_test_cache(test, 8 + prandom_u32_max(300), 0, (iter & 1) ? ctor_set_x : NULL); void *objects[] = { - test_alloc(test, size, GFP_KERNEL, ALLOCATE_RIGHT), - test_alloc(test, size, GFP_KERNEL, ALLOCATE_NONE), - test_alloc(test, size, GFP_KERNEL, ALLOCATE_LEFT), - test_alloc(test, size, GFP_KERNEL, ALLOCATE_NONE), - test_alloc(test, size, GFP_KERNEL, ALLOCATE_NONE), + test_alloc(test, 32, GFP_KERNEL, ALLOCATE_RIGHT), + test_alloc(test, 32, GFP_KERNEL, ALLOCATE_NONE), + test_alloc(test, 32, GFP_KERNEL, ALLOCATE_LEFT), + test_alloc(test, 32, GFP_KERNEL, ALLOCATE_NONE), + test_alloc(test, 32, GFP_KERNEL, ALLOCATE_NONE), }; kmem_cache_free_bulk(test_cache, ARRAY_SIZE(objects), objects); Is gcc-10.3.0 simply confused? test_out_of_bounds_read() is clearly calling kmalloc_index(32) which is OK. Anyway, I'll drop this patch for now so I can compile a kernel! From: Hyeonggon Yoo <42.hyeyoo@gmail.com> Subject: mm, slub: change run-time assertion in kmalloc_index() to compile-time Currently when size is not supported by kmalloc_index, compiler will generate a run-time BUG() while compile-time error is also possible, and better. So change BUG to BUILD_BUG_ON_MSG to make compile-time check possible. Also remove code that allocates more than 32MB because current implementation supports only up to 32MB. Link: https://lkml.kernel.org/r/20210511173448.GA54466@hyeyoo Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Reviewed-by: Vlastimil Babka Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton --- include/linux/slab.h | 7 +++++-- mm/slab_common.c | 7 +++---- 2 files changed, 8 insertions(+), 6 deletions(-) --- a/include/linux/slab.h~mm-slub-change-run-time-assertion-in-kmalloc_index-to-compile-time +++ a/include/linux/slab.h @@ -346,6 +346,9 @@ static __always_inline enum kmalloc_cach * 1 = 65 .. 96 bytes * 2 = 129 .. 192 bytes * n = 2^(n-1)+1 .. 2^n + * + * Note: there's no need to optimize kmalloc_index because it's evaluated + * in compile-time. */ static __always_inline unsigned int kmalloc_index(size_t size) { @@ -382,8 +385,8 @@ static __always_inline unsigned int kmal if (size <= 8 * 1024 * 1024) return 23; if (size <= 16 * 1024 * 1024) return 24; if (size <= 32 * 1024 * 1024) return 25; - if (size <= 64 * 1024 * 1024) return 26; - BUG(); + + BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()"); /* Will never be reached. Needed because the compiler may complain */ return -1; --- a/mm/slab_common.c~mm-slub-change-run-time-assertion-in-kmalloc_index-to-compile-time +++ a/mm/slab_common.c @@ -755,8 +755,8 @@ struct kmem_cache *kmalloc_slab(size_t s /* * kmalloc_info[] is to make slub_debug=,kmalloc-xx option work at boot time. - * kmalloc_index() supports up to 2^26=64MB, so the final entry of the table is - * kmalloc-67108864. + * kmalloc_index() supports up to 2^25=32MB, so the final entry of the table is + * kmalloc-32M. */ const struct kmalloc_info_struct kmalloc_info[] __initconst = { INIT_KMALLOC_INFO(0, 0), @@ -784,8 +784,7 @@ const struct kmalloc_info_struct kmalloc INIT_KMALLOC_INFO(4194304, 4M), INIT_KMALLOC_INFO(8388608, 8M), INIT_KMALLOC_INFO(16777216, 16M), - INIT_KMALLOC_INFO(33554432, 32M), - INIT_KMALLOC_INFO(67108864, 64M) + INIT_KMALLOC_INFO(33554432, 32M) }; /* _