linux-kernel - Re: [PATCH v6 1/4] mm/slub: enable debugging memory wasting of kmalloc

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Date:   Thu, 3 Nov 2022 22:16:12 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     John Thomson <lists@...nthomson.fastmail.com.au>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Christoph Lameter" <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "Jonathan Corbet" <corbet@....net>,
        Andrey Konovalov <andreyknvl@...il.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        Robin Murphy <robin.murphy@....com>,
        John Garry <john.garry@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
Subject: Re: [PATCH v6 1/4] mm/slub: enable debugging memory wasting of
 kmalloc

On Thu, Nov 03, 2022 at 09:33:28AM +0100, Vlastimil Babka wrote:
[...]
> >> AFAICS before this patch, we "survive" "kmem_cache *s" being NULL as
> >> slab_pre_alloc_hook() will happen to return NULL and we bail out from
> >> slab_alloc_node(). But this is a side-effect, not an intended protection.
> >> Also the CONFIG_TRACING variant of kmalloc_trace() would have called
> >> trace_kmalloc dereferencing s->size anyway even before this patch.
> >> 
> >> I don't think we should add WARNS in the slab hot paths just to prevent this
> >> rare error of using slab too early. At most VM_WARN... would be acceptable
> >> but still not necessary as crashing immediately from a NULL pointer is
> >> sufficient.
> >> 
> >> So IMHO mips should fix their soc init, 
> > 
> > Yes, for the mips fix, John has proposed to defer the calling of prom_soc_init(),
> > which looks reasonable.
> > 
> >> and we should look into the
> >> CONFIG_TRACING=n variant of kmalloc_trace(), to pass orig_size properly.
> > 
> > You mean check if the pointer is NULL and bail out early. 
> 
> No I mean here:
> 
> #else /* CONFIG_TRACING */
> /* Save a function call when CONFIG_TRACING=n */
> static __always_inline __alloc_size(3)                                   
> void *kmalloc_trace(struct kmem_cache *s, gfp_t flags, size_t size)
> {       
>         void *ret = kmem_cache_alloc(s, flags);
>                     
>         ret = kasan_kmalloc(s, ret, size, flags);
>         return ret;
> }
> 
> we call kmem_cache_alloc() and discard the size parameter, so it will assume
> s->object_size (and as the side-effect, crash if s is NULL). We shouldn't
> add "s is NULL?" checks, but fix passing the size - probably switch to
> __kmem_cache_alloc_node()? and in the following kmalloc_node_trace() analogically.
 
Got it, thanks! I might have missed it during some rebasing for the
kmalloc wastage debug patch.

How about the following fix?

Thanks,
Feng

---
>From 9f9fa9da8946fd44625f873c0f51167357075be1 Mon Sep 17 00:00:00 2001
From: Feng Tang <feng.tang@...el.com>
Date: Thu, 3 Nov 2022 21:32:10 +0800
Subject: [PATCH] mm/slub: Add missing orig_size parameter for wastage debug

commit 6edf2576a6cc ("mm/slub: enable debugging memory wasting of
kmalloc") was introduced for debugging kmalloc memory wastage,
and it missed to pass the original request size for kmalloc_trace()
and kmalloc_node_trace() in CONFIG_TRACING=n path.

Fix it by using __kmem_cache_alloc_node() with correct original
request size.

Fixes: 6edf2576a6cc ("mm/slub: enable debugging memory wasting of kmalloc")
Suggested-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Feng Tang <feng.tang@...el.com>
---
 include/linux/slab.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 90877fcde70b..9691afa569e1 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -469,6 +469,9 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node) __assume_kmalloc_alignm
 							 __alloc_size(1);
 void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t flags, int node) __assume_slab_alignment
 									 __malloc;
+void *__kmem_cache_alloc_node(struct kmem_cache *s, gfp_t flags, int node,
+				size_t orig_size, unsigned long caller) __assume_slab_alignment
+									 __malloc;
 
 #ifdef CONFIG_TRACING
 void *kmalloc_trace(struct kmem_cache *s, gfp_t flags, size_t size)
@@ -482,7 +485,8 @@ void *kmalloc_node_trace(struct kmem_cache *s, gfp_t gfpflags,
 static __always_inline __alloc_size(3)
 void *kmalloc_trace(struct kmem_cache *s, gfp_t flags, size_t size)
 {
-	void *ret = kmem_cache_alloc(s, flags);
+	void *ret = __kmem_cache_alloc_node(s, flags, NUMA_NO_NODE,
+					    size, _RET_IP_);
 
 	ret = kasan_kmalloc(s, ret, size, flags);
 	return ret;
@@ -492,7 +496,8 @@ static __always_inline __alloc_size(4)
 void *kmalloc_node_trace(struct kmem_cache *s, gfp_t gfpflags,
 			 int node, size_t size)
 {
-	void *ret = kmem_cache_alloc_node(s, gfpflags, node);
+	void *ret = __kmem_cache_alloc_node(s, gfpflags, node,
+					    size, _RET_IP_);
 
 	ret = kasan_kmalloc(s, ret, size, gfpflags);
 	return ret;
-- 
2.34.1