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Date:   Tue, 1 Nov 2022 18:31:47 +0900
From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
To:     John Thomson <lists@johnthomson.fastmail.com.au>
Cc:     Feng Tang <feng.tang@intel.com>, Vlastimil Babka <vbabka@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Dmitry Vyukov <dvyukov@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kasan-dev@googlegroups.com" <kasan-dev@googlegroups.com>,
        Robin Murphy <robin.murphy@arm.com>,
        John Garry <john.garry@huawei.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-mips@vger.kernel.org
Subject: Re: [PATCH v6 1/4] mm/slub: enable debugging memory wasting of
 kmalloc
Message-ID: <Y2DngwUc7cLB0dG7@hyeyoo>
References: <20220913065423.520159-1-feng.tang@intel.com>
 <20220913065423.520159-2-feng.tang@intel.com>
 <becf2ac3-2a90-4f3a-96d9-a70f67c66e4a@app.fastmail.com>
 <af2ba83d-c3f4-c6fb-794e-c2c7c0892c44@suse.cz>
 <Y180l6zUnNjdCoaE@feng-clx>
 <c4285caf-277c-45fd-8fc7-8a1d61685ce8@app.fastmail.com>
 <Y1+0sbQ3R4DB46NX@feng-clx>
 <9b71ae3e-7f53-4c9e-90c4-79d3d649f94c@app.fastmail.com>
 <Y2DReuPHZungAGsU@feng-clx>
 <53b53476-bb1e-402e-9f65-fd7f0ecf94c2@app.fastmail.com>
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On Tue, Nov 01, 2022 at 09:20:21AM +0000, John Thomson wrote:
> On Tue, 1 Nov 2022, at 07:57, Feng Tang wrote:
> > Hi Thomson,
> >
> > Thanks for testing!
> >
> > + mips maintainer and mail list. The original report is here
> >
> > https://lore.kernel.org/lkml/becf2ac3-2a90-4f3a-96d9-a70f67c66e4a@app.fastmail.com/
>
> I am guessing my issue comes from __kmem_cache_alloc_lru accessing s->object_size when (kmem_cache) s is NULL?
> If that is the case, this change is not to blame, it only exposes the issue?
> 
> I get the following dmesg (note very early NULL kmem_cache) with the below change atop v6.1-rc3:
> 
> transfer started ......................................... transfer ok, time=2.02s
> setting up elf image... OK
> jumping to kernel code
> zimage at:     80B842A0 810B4EFC
> 
> Uncompressing Linux at load address 80001000
> 
> Copy device tree to address  80B80EE0
> 
> Now, booting the kernel...
> 
> [    0.000000] Linux version 6.1.0-rc3+ (john@john) (mipsel-buildroot-linux-gnu-gcc.br_real (Buildroot 2021.11-4428-g6b6741b) 12.2.0, GNU ld (GNU Binutils) 2.39) #61 SMP Tue Nov  1 18:04:13 AEST 2022
> [    0.000000] slub: kmem_cache_alloc called with kmem_cache: 0x0
> [    0.000000] slub: __kmem_cache_alloc_lru called with kmem_cache: 0x0
> [    0.000000] SoC Type: MediaTek MT7621 ver:1 eco:3
> [    0.000000] printk: bootconsole [early0] enabled
> [    0.000000] CPU0 revision is: 0001992f (MIPS 1004Kc)
> [    0.000000] MIPS: machine is MikroTik RouterBOARD 760iGS
> 
> normal boot
> 
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 157527d7101b..10fcdf2520d2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3410,7 +3410,13 @@ static __always_inline
>  void *__kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
>  			     gfp_t gfpflags)
>  {
> -	void *ret = slab_alloc(s, lru, gfpflags, _RET_IP_, s->object_size);
> +	void *ret;
> +	if (IS_ERR_OR_NULL(s)) {
> +		pr_warn("slub: __kmem_cache_alloc_lru called with kmem_cache: %pSR\n", s);
> +		ret = slab_alloc(s, lru, gfpflags, _RET_IP_, 0);
> +	} else {
> +		ret = slab_alloc(s, lru, gfpflags, _RET_IP_, s->object_size);
> +	}
>  
>  	trace_kmem_cache_alloc(_RET_IP_, ret, s, gfpflags, NUMA_NO_NODE);
>  
> @@ -3419,6 +3425,8 @@ void *__kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
>  
>  void *kmem_cache_alloc(struct kmem_cache *s, gfp_t gfpflags)
>  {
> +	if (IS_ERR_OR_NULL(s))
> +		pr_warn("slub: kmem_cache_alloc called with kmem_cache: %pSR\n", s);
>  	return __kmem_cache_alloc_lru(s, NULL, gfpflags);
>  }
>  EXPORT_SYMBOL(kmem_cache_alloc);
> @@ -3426,6 +3434,8 @@ EXPORT_SYMBOL(kmem_cache_alloc);
>  void *kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
>  			   gfp_t gfpflags)
>  {
> +	if (IS_ERR_OR_NULL(s))
> +		pr_warn("slub: __kmem_cache_alloc_lru called with kmem_cache: %pSR\n", s);
>  	return __kmem_cache_alloc_lru(s, lru, gfpflags);
>  }
>  EXPORT_SYMBOL(kmem_cache_alloc_lru);
> 
> 
> Any hints on where kmem_cache_alloc would be being called from this early?
> I will start looking from /init/main.c around pr_notice("%s", linux_banner);

Great. Would you try calling dump_stack(); when we observed s == NULL?
That would give more information about who passed s == NULL to these
functions.

-- 
Thanks,
Hyeonggon