linux-kernel - Re: [PATCH v5 2/3] mm/slub, kunit: add a KUnit test for SLUB debugging functionality

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Date:   Wed, 12 May 2021 21:44:40 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     glittao@...il.com
Cc:     brendanhiggins@...gle.com, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com, vbabka@...e.cz,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-mm@...ck.org, elver@...gle.com,
        dlatypov@...gle.com
Subject: Re: [PATCH v5 2/3] mm/slub, kunit: add a KUnit test for SLUB
 debugging functionality

On Tue, 11 May 2021 17:07:33 +0200 glittao@...il.com wrote:

> From: Oliver Glitta <glittao@...il.com>
> 
> SLUB has resiliency_test() function which is hidden behind #ifdef
> SLUB_RESILIENCY_TEST that is not part of Kconfig, so nobody
> runs it. KUnit should be a proper replacement for it.
> 
> Try changing byte in redzone after allocation and changing
> pointer to next free node, first byte, 50th byte and redzone
> byte. Check if validation finds errors.
> 
> There are several differences from the original resiliency test:
> Tests create own caches with known state instead of corrupting
> shared kmalloc caches.
> 
> The corruption of freepointer uses correct offset, the original
> resiliency test got broken with freepointer changes.
> 
> Scratch changing random byte test, because it does not have
> meaning in this form where we need deterministic results.
> 
> Add new option CONFIG_SLUB_KUNIT_TEST in Kconfig.
> Tests next_pointer, first_word and clobber_50th_byte do not run
> with KASAN option on. Because the test deliberately modifies non-allocated
> objects.
> 
> Use kunit_resource to count errors in cache and silence bug reports.
> Count error whenever slab_bug() or slab_fix() is called or when
> the count of pages is wrong.
> 
> ...
>
>  lib/slub_kunit.c  | 155 ++++++++++++++++++++++++++++++++++++++++++++++
>  mm/slab.h         |   1 +
>  mm/slub.c         |  46 +++++++++++++-
>  5 files changed, 212 insertions(+), 3 deletions(-)
>  create mode 100644 lib/slub_kunit.c
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 678c13967580..7723f58a9394 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2429,6 +2429,18 @@ config BITS_TEST
> 
>  	  If unsure, say N.
> 
> +config SLUB_KUNIT_TEST
> +	tristate "KUnit test for SLUB cache error detection" if !KUNIT_ALL_TESTS

This means it can be compiled as a kernel module.  Did you runtime test the
code as a module?

ERROR: modpost: "kasan_enable_current" [lib/slub_kunit.ko] undefined!
ERROR: modpost: "kasan_disable_current" [lib/slub_kunit.ko] undefined!

--- a/mm/kasan/common.c~a
+++ a/mm/kasan/common.c
@@ -51,11 +51,14 @@ void kasan_enable_current(void)
 {
 	current->kasan_depth++;
 }
+EXPORT_SYMBOL(kasan_enable_current);
 
 void kasan_disable_current(void)
 {
 	current->kasan_depth--;
 }
+EXPORT_SYMBOL(kasan_disable_current);
+
 #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
 
 void __kasan_unpoison_range(const void *address, size_t size)
_