linux-kernel - Re: [PATCH v2 08/23] mm/slab_common: make kmalloc_large_node() consistent with kmalloc

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Date:   Tue, 26 Apr 2022 19:15:06 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Marco Elver <elver@...gle.com>,
        Matthew WilCox <willy@...radead.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 08/23] mm/slab_common: make kmalloc_large_node()
 consistent with kmalloc_large()

On 4/14/22 10:57, Hyeonggon Yoo wrote:
> Move tracepoints into kmalloc_large_node() and add missing flag fix code.
> 
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>

Hm so there's a problem with the tracepoint's caller.

kmalloc_large() is only called from kmalloc() which is an inline  thus the
callsite of kmalloc() calls directly kmalloc_large(). So when
kmalloc_large() does "trace_kmalloc(_RET_IP_, ...)" the _RET_IP_ is the
callsite of kmalloc(), which is what we want.

But with kmalloc_large_node()...

> ---
>  mm/slab_common.c |  6 ++++++
>  mm/slub.c        | 22 ++++------------------
>  2 files changed, 10 insertions(+), 18 deletions(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index e72089515030..cf17be8cd9ad 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -955,6 +955,9 @@ void *kmalloc_large_node(size_t size, gfp_t flags, int node)
>  	void *ptr = NULL;
>  	unsigned int order = get_order(size);
>  
> +	if (unlikely(flags & GFP_SLAB_BUG_MASK))
> +		flags = kmalloc_fix_flags(flags);
> +
>  	flags |= __GFP_COMP;
>  	page = alloc_pages_node(node, flags, order);
>  	if (page) {
> @@ -966,6 +969,9 @@ void *kmalloc_large_node(size_t size, gfp_t flags, int node)
>  	ptr = kasan_kmalloc_large(ptr, size, flags);
>  	/* As ptr might get tagged, call kmemleak hook after KASAN. */
>  	kmemleak_alloc(ptr, size, 1, flags);
> +	trace_kmalloc_node(_RET_IP_, ptr,
> +			   size, PAGE_SIZE << order,
> +			   flags, node);

... the _RET_IP_ here would be __kmalloc_node() which is not useful.

>  	return ptr;
>  }
> diff --git a/mm/slub.c b/mm/slub.c
> index 640712706f2b..f10a892f1772 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4396,15 +4396,8 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
>  	struct kmem_cache *s;
>  	void *ret;
>  
> -	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) {
> -		ret = kmalloc_large_node(size, flags, node);
> -
> -		trace_kmalloc_node(_RET_IP_, ret,
> -				   size, PAGE_SIZE << get_order(size),
> -				   flags, node);

Here it was OK because __kmalloc_node is expanded from something inline
coming from slab.h.

> -
> -		return ret;
> -	}
> +	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
> +		return kmalloc_large_node(size, flags, node);
>  
>  	s = kmalloc_slab(size, flags);
>  
> @@ -4861,15 +4854,8 @@ void *__kmalloc_node_track_caller(size_t size, gfp_t gfpflags,
>  	struct kmem_cache *s;
>  	void *ret;
>  
> -	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) {
> -		ret = kmalloc_large_node(size, gfpflags, node);
> -
> -		trace_kmalloc_node(caller, ret,
> -				   size, PAGE_SIZE << get_order(size),
> -				   gfpflags, node);
> -
> -		return ret;
> -	}
> +	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
> +		return kmalloc_large_node(size, gfpflags, node);

And here it even forgets the 'caller'.

>  
>  	s = kmalloc_slab(size, gfpflags);
>