Re: [PATCH] mm/slub, kunit: Make slub_kunit unaffected by global slub debugging flags

[Vlastimil Babka <vbabka@suse.cz>]

On 3/17/22 09:10, Hyeonggon Yoo wrote:
> slub_kunit does not expect other debugging flags to be set when running
> tests. When SLAB_RED_ZONE flag is set globally, test fails because the
> flag affects number of errors reported.
> 
> To make slub_kunit unaffected by global slub debugging flags, introduce
> SLAB_NO_GLOBAL_FLAGS to ignore them. It's still allowed to specify
> debugging flags by specifying cache name(s) in slub_debug parameter.

Given how we support globbing, I think it would be safest to just ignore
everything that comes from slub_debug parameter when the
SLAB_NO_GLOBAL_FLAGS flag is specified, even if it involves a (partial)
cache name match.
Maybe name it SLAB_NO_USER_FLAGS then?

> Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> ---
>  include/linux/slab.h |  3 +++
>  lib/slub_kunit.c     | 10 +++++-----
>  mm/slab.h            |  5 +++--
>  mm/slub.c            |  3 +++
>  4 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 0381868e5118..11fe2c28422d 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -112,6 +112,9 @@
>  #define SLAB_KASAN		0
>  #endif
>  
> +/* Ignore globally specified debugging flags */

I'd add that this is intended for caches created for self-tests so they
always have flags as specified in the code.

> +#define SLAB_NO_GLOBAL_FLAGS	((slab_flags_t __force)0x10000000U)
> +
>  /* The following flags affect the page allocator grouping pages by mobility */
>  /* Objects are reclaimable */
>  #define SLAB_RECLAIM_ACCOUNT	((slab_flags_t __force)0x00020000U)
> diff --git a/lib/slub_kunit.c b/lib/slub_kunit.c
> index 8662dc6cb509..acf061dc558d 100644
> --- a/lib/slub_kunit.c
> +++ b/lib/slub_kunit.c
> @@ -12,7 +12,7 @@ static int slab_errors;
>  static void test_clobber_zone(struct kunit *test)
>  {
>  	struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_alloc", 64, 0,
> -				SLAB_RED_ZONE, NULL);
> +				SLAB_RED_ZONE|SLAB_NO_GLOBAL_FLAGS, NULL);
>  	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>  
>  	kasan_disable_current();
> @@ -30,7 +30,7 @@ static void test_clobber_zone(struct kunit *test)
>  static void test_next_pointer(struct kunit *test)
>  {
>  	struct kmem_cache *s = kmem_cache_create("TestSlub_next_ptr_free", 64, 0,
> -				SLAB_POISON, NULL);
> +				SLAB_POISON|SLAB_NO_GLOBAL_FLAGS, NULL);
>  	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>  	unsigned long tmp;
>  	unsigned long *ptr_addr;
> @@ -75,7 +75,7 @@ static void test_next_pointer(struct kunit *test)
>  static void test_first_word(struct kunit *test)
>  {
>  	struct kmem_cache *s = kmem_cache_create("TestSlub_1th_word_free", 64, 0,
> -				SLAB_POISON, NULL);
> +				SLAB_POISON|SLAB_NO_GLOBAL_FLAGS, NULL);
>  	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>  
>  	kmem_cache_free(s, p);
> @@ -90,7 +90,7 @@ static void test_first_word(struct kunit *test)
>  static void test_clobber_50th_byte(struct kunit *test)
>  {
>  	struct kmem_cache *s = kmem_cache_create("TestSlub_50th_word_free", 64, 0,
> -				SLAB_POISON, NULL);
> +				SLAB_POISON|SLAB_NO_GLOBAL_FLAGS, NULL);
>  	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>  
>  	kmem_cache_free(s, p);
> @@ -106,7 +106,7 @@ static void test_clobber_50th_byte(struct kunit *test)
>  static void test_clobber_redzone_free(struct kunit *test)
>  {
>  	struct kmem_cache *s = kmem_cache_create("TestSlub_RZ_free", 64, 0,
> -				SLAB_RED_ZONE, NULL);
> +				SLAB_RED_ZONE|SLAB_NO_GLOBAL_FLAGS, NULL);
>  	u8 *p = kmem_cache_alloc(s, GFP_KERNEL);
>  
>  	kasan_disable_current();
> diff --git a/mm/slab.h b/mm/slab.h
> index c7f2abc2b154..69946131208a 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -330,7 +330,7 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
>  			  SLAB_ACCOUNT)
>  #elif defined(CONFIG_SLUB)
>  #define SLAB_CACHE_FLAGS (SLAB_NOLEAKTRACE | SLAB_RECLAIM_ACCOUNT | \
> -			  SLAB_TEMPORARY | SLAB_ACCOUNT)
> +			  SLAB_TEMPORARY | SLAB_ACCOUNT | SLAB_NO_GLOBAL_FLAGS)
>  #else
>  #define SLAB_CACHE_FLAGS (SLAB_NOLEAKTRACE)
>  #endif
> @@ -349,7 +349,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
>  			      SLAB_NOLEAKTRACE | \
>  			      SLAB_RECLAIM_ACCOUNT | \
>  			      SLAB_TEMPORARY | \
> -			      SLAB_ACCOUNT)
> +			      SLAB_ACCOUNT | \
> +			      SLAB_NO_GLOBAL_FLAGS)
>  
>  bool __kmem_cache_empty(struct kmem_cache *);
>  int __kmem_cache_shutdown(struct kmem_cache *);
> diff --git a/mm/slub.c b/mm/slub.c
> index 71e8663f6037..2a3cffd7b27f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1592,6 +1592,9 @@ slab_flags_t kmem_cache_flags(unsigned int object_size,
>  	if (flags & SLAB_NOLEAKTRACE)
>  		slub_debug_local &= ~SLAB_STORE_USER;
>  
> +	if (flags & SLAB_NO_GLOBAL_FLAGS)
> +		slub_debug_local = 0;
> +
>  	len = strlen(name);
>  	next_block = slub_debug_string;
>  	/* Go through all blocks of debug options, see if any matches our slab's name */