Re: [PATCH v3] mm, slub: change run-time assertion in kmalloc_index() to compile-time
From: Hyeonggon Yoo <hidden>
Date: 2021-05-13 12:03:59
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On Thu, May 13, 2021 at 12:31:38PM +0200, Marco Elver wrote:
quoted hunk ↗ jump to hunk
------ >8 ------ From: Marco Elver <elver@google.com> Subject: [PATCH] kfence: test: fix for "mm, slub: change run-time assertion in kmalloc_index() to compile-time" Signed-off-by: Marco Elver <elver@google.com> --- include/linux/slab.h | 9 +++++++-- mm/kfence/kfence_test.c | 5 +++-- 2 files changed, 10 insertions(+), 4 deletions(-)diff --git a/include/linux/slab.h b/include/linux/slab.h index 27d142564557..7a10bdc4b7a9 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h@@ -350,7 +350,8 @@ static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags) * 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) +static __always_inline unsigned int __kmalloc_index(size_t size, + bool size_is_constant) { if (!size) return 0;@@ -386,11 +387,15 @@ static __always_inline unsigned int kmalloc_index(size_t size) if (size <= 16 * 1024 * 1024) return 24; if (size <= 32 * 1024 * 1024) return 25; - BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()"); + if (size_is_constant) + BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()"); + else + BUG();
what about checking size it on top of kmalloc_index? because by definition of KMALLOC_SHIFT_HIGH, it's not always 25. it can be less than 25. for some situations. below is what I suggested beofre. for just reference:
--- include/linux/slab.h.orig 2021-05-12 17:56:54.504738768 +0900
+++ include/linux/slab.h 2021-05-13 15:06:25.724565850 +0900@@ -346,9 +346,18 @@ 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) { + if (__builtin_constant_p(size)) { + BUILD_BUG_ON_MSG(size > KMALLOC_MAX_CACHE_SIZE , "unexpected size in kmalloc_index()"); + } else if (size > KMALLOC_MAX_CACHE_SIZE) { + BUG(); + } + if (!size) return 0;
@@ -382,8 +391,6 @@ 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(); /* Will never be reached. Needed because the compiler may complain */ return -1;