linux-kernel - Re: [PATCH] slab: remove store

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Date:   Tue, 16 Apr 2019 17:25:03 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Qian Cai <cai@....pw>, akpm@...ux-foundation.org
Cc:     luto@...nel.org, jpoimboe@...hat.com,
        sean.j.christopherson@...el.com, penberg@...nel.org,
        rientjes@...gle.com, tglx@...utronix.de, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slab: remove store_stackinfo()

On 4/16/19 4:22 PM, Qian Cai wrote:
> store_stackinfo() does not seem used in actual SLAB debugging.
> Potentially, it could be added to check_poison_obj() to provide more
> information, but this seems like an overkill due to the declining
> popularity of the SLAB, so just remove it instead.
> 
> Signed-off-by: Qian Cai <cai@....pw>

I've acked Thomas' version already which was narrower, but no objection
to remove more stuff on top of that. Linus (and I later in another
thread) already pointed out /proc/slab_allocators. It only takes a look
at add_caller() there to not regret removing that one.

> ---
>  mm/slab.c | 48 ++++++------------------------------------------
>  1 file changed, 6 insertions(+), 42 deletions(-)
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index 3e1b7ff0360c..20f318f4f56e 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1467,53 +1467,17 @@ static bool is_debug_pagealloc_cache(struct kmem_cache *cachep)
>  }
>  
>  #ifdef CONFIG_DEBUG_PAGEALLOC
> -static void store_stackinfo(struct kmem_cache *cachep, unsigned long *addr,
> -			    unsigned long caller)
> -{
> -	int size = cachep->object_size;
> -
> -	addr = (unsigned long *)&((char *)addr)[obj_offset(cachep)];
> -
> -	if (size < 5 * sizeof(unsigned long))
> -		return;
> -
> -	*addr++ = 0x12345678;
> -	*addr++ = caller;
> -	*addr++ = smp_processor_id();
> -	size -= 3 * sizeof(unsigned long);
> -	{
> -		unsigned long *sptr = &caller;
> -		unsigned long svalue;
> -
> -		while (!kstack_end(sptr)) {
> -			svalue = *sptr++;
> -			if (kernel_text_address(svalue)) {
> -				*addr++ = svalue;
> -				size -= sizeof(unsigned long);
> -				if (size <= sizeof(unsigned long))
> -					break;
> -			}
> -		}
> -
> -	}
> -	*addr++ = 0x87654321;
> -}
> -
> -static void slab_kernel_map(struct kmem_cache *cachep, void *objp,
> -				int map, unsigned long caller)
> +static void slab_kernel_map(struct kmem_cache *cachep, void *objp, int map)
>  {
>  	if (!is_debug_pagealloc_cache(cachep))
>  		return;
>  
> -	if (caller)
> -		store_stackinfo(cachep, objp, caller);
> -
>  	kernel_map_pages(virt_to_page(objp), cachep->size / PAGE_SIZE, map);
>  }
>  
>  #else
>  static inline void slab_kernel_map(struct kmem_cache *cachep, void *objp,
> -				int map, unsigned long caller) {}
> +				int map) {}
>  
>  #endif
>  
> @@ -1661,7 +1625,7 @@ static void slab_destroy_debugcheck(struct kmem_cache *cachep,
>  
>  		if (cachep->flags & SLAB_POISON) {
>  			check_poison_obj(cachep, objp);
> -			slab_kernel_map(cachep, objp, 1, 0);
> +			slab_kernel_map(cachep, objp, 1);
>  		}
>  		if (cachep->flags & SLAB_RED_ZONE) {
>  			if (*dbg_redzone1(cachep, objp) != RED_INACTIVE)
> @@ -2433,7 +2397,7 @@ static void cache_init_objs_debug(struct kmem_cache *cachep, struct page *page)
>  		/* need to poison the objs? */
>  		if (cachep->flags & SLAB_POISON) {
>  			poison_obj(cachep, objp, POISON_FREE);
> -			slab_kernel_map(cachep, objp, 0, 0);
> +			slab_kernel_map(cachep, objp, 0);
>  		}
>  	}
>  #endif
> @@ -2812,7 +2776,7 @@ static void *cache_free_debugcheck(struct kmem_cache *cachep, void *objp,
>  
>  	if (cachep->flags & SLAB_POISON) {
>  		poison_obj(cachep, objp, POISON_FREE);
> -		slab_kernel_map(cachep, objp, 0, caller);
> +		slab_kernel_map(cachep, objp, 0);
>  	}
>  	return objp;
>  }
> @@ -3076,7 +3040,7 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
>  		return objp;
>  	if (cachep->flags & SLAB_POISON) {
>  		check_poison_obj(cachep, objp);
> -		slab_kernel_map(cachep, objp, 1, 0);
> +		slab_kernel_map(cachep, objp, 1);
>  		poison_obj(cachep, objp, POISON_INUSE);
>  	}
>  	if (cachep->flags & SLAB_STORE_USER)
>