Re: [PATCH 1/2] selftests: add a kselftest for SLUB debugging functionality

[Marco Elver]

On Tue, Mar 16, 2021 at 01:41PM +0100, glittao@xxxxxxxxx wrote:
> From: Oliver Glitta <glittao@xxxxxxxxx>
> 
> SLUB has resiliency_test() function which is hidden behind #ifdef
> SLUB_RESILIENCY_TEST that is not part of Kconfig, so nobody
> runs it. Kselftest should 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_TEST_SLUB in Kconfig.
> 
> Add parameter to function validate_slab_cache() to return
> number of errors in cache.
> 
> Signed-off-by: Oliver Glitta <glittao@xxxxxxxxx>

No objection per-se, but have you considered a KUnit-based test instead?

There is no user space portion required to run this test, and a pure
in-kernel KUnit test would be cleaner. Various boiler-plate below,
including pr_err()s, the kselftest script etc. would simply not be
necessary.

This is only a suggestion, but just want to make sure you've considered
the option and weighed its pros/cons.

Thanks,
-- Marco

> ---
>  lib/Kconfig.debug                    |   4 +
>  lib/Makefile                         |   1 +
>  lib/test_slub.c                      | 125 +++++++++++++++++++++++++++
>  mm/slab.h                            |   1 +
>  mm/slub.c                            |  34 +++++---
>  tools/testing/selftests/lib/Makefile |   2 +-
>  tools/testing/selftests/lib/config   |   1 +
>  tools/testing/selftests/lib/slub.sh  |   3 +
>  8 files changed, 159 insertions(+), 12 deletions(-)
>  create mode 100644 lib/test_slub.c
>  create mode 100755 tools/testing/selftests/lib/slub.sh
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 2779c29d9981..2d56092abbc4 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2123,6 +2123,10 @@ config TEST_KSTRTOX
>  config TEST_PRINTF
>  	tristate "Test printf() family of functions at runtime"
>  
> +config TEST_SLUB
> +	tristate "Test SLUB cache errors at runtime"
> +	depends on SLUB_DEBUG
> +
>  config TEST_BITMAP
>  	tristate "Test bitmap_*() family of functions at runtime"
>  	help
> diff --git a/lib/Makefile b/lib/Makefile
> index b5307d3eec1a..b6603803b1c4 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -83,6 +83,7 @@ obj-$(CONFIG_TEST_USER_COPY) += test_user_copy.o
>  obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_keys.o
>  obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_key_base.o
>  obj-$(CONFIG_TEST_PRINTF) += test_printf.o
> +obj-$(CONFIG_TEST_SLUB) += test_slub.o
>  obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
>  obj-$(CONFIG_TEST_STRSCPY) += test_strscpy.o
>  obj-$(CONFIG_TEST_UUID) += test_uuid.o
> diff --git a/lib/test_slub.c b/lib/test_slub.c
> new file mode 100644
> index 000000000000..0075d9b44251
> --- /dev/null
> +++ b/lib/test_slub.c
> @@ -0,0 +1,125 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Test cases for slub facility.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/mm.h>
> +#include <linux/slab.h>
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include "../mm/slab.h"
> +
> +#include "../tools/testing/selftests/kselftest_module.h"
> +
> +
> +KSTM_MODULE_GLOBALS();
> +
> +
> +static void __init validate_result(struct kmem_cache *s, int expected_errors)
> +{
> +	int errors = 0;
> +
> +	validate_slab_cache(s, &errors);
> +	KSTM_CHECK_ZERO(errors - expected_errors);
> +}
> +
> +static void __init test_clobber_zone(void)
> +{
> +	struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_alloc", 64, 0,
> +				SLAB_RED_ZONE, NULL);
> +	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
> +
> +	p[64] = 0x12;
> +	pr_err("1. kmem_cache: Clobber Redzone 0x12->0x%p\n", p + 64);
> +
> +	validate_result(s, 1);
> +	kmem_cache_free(s, p);
> +	kmem_cache_destroy(s);
> +}
> +
> +static void __init test_next_pointer(void)
> +{
> +	struct kmem_cache *s = kmem_cache_create("TestSlub_next_ptr_free", 64, 0,
> +				SLAB_RED_ZONE, NULL);
> +	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
> +
> +	kmem_cache_free(s, p);
> +	p[s->offset] = 0x12;
> +	pr_err("1. kmem_cache: Clobber next pointer 0x34 -> -0x%p\n", p);
> +
> +	validate_result(s, 1);
> +	kmem_cache_destroy(s);
> +}
> +
> +static void __init test_first_word(void)
> +{
> +	struct kmem_cache *s = kmem_cache_create("TestSlub_1th_word_free", 64, 0,
> +				SLAB_POISON, NULL);
> +	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
> +
> +	kmem_cache_free(s, p);
> +	*p = 0x78;
> +	pr_err("2. kmem_cache: Clobber first word 0x78->0x%p\n", p);
> +
> +	validate_result(s, 1);
> +	kmem_cache_destroy(s);
> +}
> +
> +static void __init test_clobber_50th_byte(void)
> +{
> +	struct kmem_cache *s = kmem_cache_create("TestSlub_50th_word_free", 64, 0,
> +				SLAB_POISON, NULL);
> +	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
> +
> +	kmem_cache_free(s, p);
> +	p[50] = 0x9a;
> +	pr_err("3. kmem_cache: Clobber 50th byte 0x9a->0x%p\n", p);
> +
> +	validate_result(s, 1);
> +	kmem_cache_destroy(s);
> +}
> +
> +static void __init test_clobber_redzone_free(void)
> +{
> +	struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_free", 64, 0,
> +				SLAB_RED_ZONE, NULL);
> +	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
> +
> +	kmem_cache_free(s, p);
> +	p[64] = 0xab;
> +	pr_err("4. kmem_cache: Clobber redzone 0xab->0x%p\n", p);
> +
> +	validate_result(s, 1);
> +	kmem_cache_destroy(s);
> +}
> +
> +static void __init resiliency_test(void)
> +{
> +
> +	BUILD_BUG_ON(KMALLOC_MIN_SIZE > 16 || KMALLOC_SHIFT_HIGH < 10);
> +
> +	pr_err("SLUB resiliency testing\n");
> +	pr_err("-----------------------\n");
> +	pr_err("A. Corruption after allocation\n");
> +
> +	test_clobber_zone();
> +
> +	pr_err("\nB. Corruption after free\n");
> +
> +	test_next_pointer();
> +	test_first_word();
> +	test_clobber_50th_byte();
> +	test_clobber_redzone_free();
> +}
> +
> +
> +static void __init selftest(void)
> +{
> +	resiliency_test();
> +}
> +
> +
> +KSTM_MODULE_LOADERS(test_slub);
> +MODULE_LICENSE("GPL");
> diff --git a/mm/slab.h b/mm/slab.h
> index 076582f58f68..5fc18d506b3b 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -215,6 +215,7 @@ DECLARE_STATIC_KEY_TRUE(slub_debug_enabled);
>  DECLARE_STATIC_KEY_FALSE(slub_debug_enabled);
>  #endif
>  extern void print_tracking(struct kmem_cache *s, void *object);
> +long validate_slab_cache(struct kmem_cache *s, int *errors);
>  #else
>  static inline void print_tracking(struct kmem_cache *s, void *object)
>  {
> diff --git a/mm/slub.c b/mm/slub.c
> index e26c274b4657..c00e2b263e03 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4612,7 +4612,8 @@ static int count_total(struct page *page)
>  #endif
>  
>  #ifdef CONFIG_SLUB_DEBUG
> -static void validate_slab(struct kmem_cache *s, struct page *page)
> +static void validate_slab(struct kmem_cache *s, struct page *page,
> +						int *errors)
>  {
>  	void *p;
>  	void *addr = page_address(page);
> @@ -4620,8 +4621,10 @@ static void validate_slab(struct kmem_cache *s, struct page *page)
>  
>  	slab_lock(page);
>  
> -	if (!check_slab(s, page) || !on_freelist(s, page, NULL))
> +	if (!check_slab(s, page) || !on_freelist(s, page, NULL)) {
> +		*errors += 1;
>  		goto unlock;
> +	}
>  
>  	/* Now we know that a valid freelist exists */
>  	map = get_map(s, page);
> @@ -4629,8 +4632,10 @@ static void validate_slab(struct kmem_cache *s, struct page *page)
>  		u8 val = test_bit(__obj_to_index(s, addr, p), map) ?
>  			 SLUB_RED_INACTIVE : SLUB_RED_ACTIVE;
>  
> -		if (!check_object(s, page, p, val))
> +		if (!check_object(s, page, p, val)) {
> +			*errors += 1;
>  			break;
> +		}
>  	}
>  	put_map(map);
>  unlock:
> @@ -4638,7 +4643,7 @@ static void validate_slab(struct kmem_cache *s, struct page *page)
>  }
>  
>  static int validate_slab_node(struct kmem_cache *s,
> -		struct kmem_cache_node *n)
> +		struct kmem_cache_node *n, int *errors)
>  {
>  	unsigned long count = 0;
>  	struct page *page;
> @@ -4647,30 +4652,34 @@ static int validate_slab_node(struct kmem_cache *s,
>  	spin_lock_irqsave(&n->list_lock, flags);
>  
>  	list_for_each_entry(page, &n->partial, slab_list) {
> -		validate_slab(s, page);
> +		validate_slab(s, page, errors);
>  		count++;
>  	}
> -	if (count != n->nr_partial)
> +	if (count != n->nr_partial) {
>  		pr_err("SLUB %s: %ld partial slabs counted but counter=%ld\n",
>  		       s->name, count, n->nr_partial);
> +		*errors += 1;
> +	}
>  
>  	if (!(s->flags & SLAB_STORE_USER))
>  		goto out;
>  
>  	list_for_each_entry(page, &n->full, slab_list) {
> -		validate_slab(s, page);
> +		validate_slab(s, page, errors);
>  		count++;
>  	}
> -	if (count != atomic_long_read(&n->nr_slabs))
> +	if (count != atomic_long_read(&n->nr_slabs)) {
>  		pr_err("SLUB: %s %ld slabs counted but counter=%ld\n",
>  		       s->name, count, atomic_long_read(&n->nr_slabs));
> +		*errors += 1;
> +	}
>  
>  out:
>  	spin_unlock_irqrestore(&n->list_lock, flags);
>  	return count;
>  }
>  
> -static long validate_slab_cache(struct kmem_cache *s)
> +long validate_slab_cache(struct kmem_cache *s, int *errors)
>  {
>  	int node;
>  	unsigned long count = 0;
> @@ -4678,10 +4687,12 @@ static long validate_slab_cache(struct kmem_cache *s)
>  
>  	flush_all(s);
>  	for_each_kmem_cache_node(s, node, n)
> -		count += validate_slab_node(s, n);
> +		count += validate_slab_node(s, n, errors);
>  
>  	return count;
>  }
> +EXPORT_SYMBOL(validate_slab_cache);
> +
>  /*
>   * Generate lists of code addresses where slabcache objects are allocated
>   * and freed.
> @@ -5336,9 +5347,10 @@ static ssize_t validate_store(struct kmem_cache *s,
>  			const char *buf, size_t length)
>  {
>  	int ret = -EINVAL;
> +	int errors = 0;
>  
>  	if (buf[0] == '1') {
> -		ret = validate_slab_cache(s);
> +		ret = validate_slab_cache(s, &errors);
>  		if (ret >= 0)
>  			ret = length;
>  	}
> diff --git a/tools/testing/selftests/lib/Makefile b/tools/testing/selftests/lib/Makefile
> index a105f094676e..f168313b7949 100644
> --- a/tools/testing/selftests/lib/Makefile
> +++ b/tools/testing/selftests/lib/Makefile
> @@ -4,6 +4,6 @@
>  # No binaries, but make sure arg-less "make" doesn't trigger "run_tests"
>  all:
>  
> -TEST_PROGS := printf.sh bitmap.sh prime_numbers.sh strscpy.sh
> +TEST_PROGS := printf.sh bitmap.sh prime_numbers.sh strscpy.sh slub.sh
>  
>  include ../lib.mk
> diff --git a/tools/testing/selftests/lib/config b/tools/testing/selftests/lib/config
> index b80ee3f6e265..4190863032e7 100644
> --- a/tools/testing/selftests/lib/config
> +++ b/tools/testing/selftests/lib/config
> @@ -3,3 +3,4 @@ CONFIG_TEST_BITMAP=m
>  CONFIG_PRIME_NUMBERS=m
>  CONFIG_TEST_STRSCPY=m
>  CONFIG_TEST_BITOPS=m
> +CONFIG_TEST_SLUB=m
> \ No newline at end of file
> diff --git a/tools/testing/selftests/lib/slub.sh b/tools/testing/selftests/lib/slub.sh
> new file mode 100755
> index 000000000000..8b5757702910
> --- /dev/null
> +++ b/tools/testing/selftests/lib/slub.sh
> @@ -0,0 +1,3 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0+
> +$(dirname $0)/../kselftest/module.sh "slub" test_slub