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Date: Thu, 3 Nov 2022 23:36:19 +0900
From: Hyeonggon Yoo <42.hyeyoo@...il.com>
To: Feng Tang <feng.tang@...el.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
John Thomson <lists@...nthomson.fastmail.com.au>,
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 10:16:12PM +0800, Feng Tang wrote:
> 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.
That was good catch and I missed too!
But FYI I'm suggesting to drop CONFIG_TRACING=n variant:
https://lore.kernel.org/linux-mm/20221101222520.never.109-kees@kernel.org/T/#m20ecf14390e406247bde0ea9cce368f469c539ed
Any thoughts?
>
> 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
>
>
>
--
Thanks,
Hyeonggon
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