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Message-ID: <097d8fba-bd10-a312-24a3-a4068c4f424c@suse.cz>
Date: Wed, 2 Nov 2022 09:22:37 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: John Thomson <lists@...nthomson.fastmail.com.au>,
Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc: Feng Tang <feng.tang@...el.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
Subject: Re: [PATCH v6 1/4] mm/slub: enable debugging memory wasting of
kmalloc
On 11/1/22 11:33, John Thomson wrote:
> On Tue, 1 Nov 2022, at 09:31, Hyeonggon Yoo wrote:
>> 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@...n) (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.
>>
>
> With the dump_stack() in place:
>
> Now, booting the kernel...
>
> [ 0.000000] Linux version 6.1.0-rc3+ (john@...n) (mipsel-buildroot-linux-gnu-gcc.br_real (Buildroot 2021.11-4428-g6b6741b) 12.2.0, GNU ld (GNU Binutils) 2.39) #62 SMP Tue Nov 1 19:49:52 AEST 2022
> [ 0.000000] slub: __kmem_cache_alloc_lru called with kmem_cache ptr: 0x0
> [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 6.1.0-rc3+ #62
> [ 0.000000] Stack : 810fff78 80084d98 80889d00 00000004 00000000 00000000 80889d5c 80c90000
> [ 0.000000] 80920000 807bd380 8089d368 80923bd3 00000000 00000001 80889d08 00000000
> [ 0.000000] 00000000 00000000 807bd380 8084bd51 00000002 00000002 00000001 6d6f4320
> [ 0.000000] 00000000 80c97ce9 80c97d14 fffffffc 807bd380 00000000 00000003 00000dc0
> [ 0.000000] 00000000 a0000000 80910000 8110a0b4 00000000 00000020 80010000 80010000
> [ 0.000000] ...
> [ 0.000000] Call Trace:
> [ 0.000000] [<80008260>] show_stack+0x28/0xf0
> [ 0.000000] [<8070cdc0>] dump_stack_lvl+0x60/0x80
> [ 0.000000] [<801c1428>] kmem_cache_alloc+0x5c0/0x740
> [ 0.000000] [<8092856c>] prom_soc_init+0x1fc/0x2b4
> [ 0.000000] [<80928060>] prom_init+0x44/0xf0
> [ 0.000000] [<80929214>] setup_arch+0x4c/0x6a8
> [ 0.000000] [<809257e0>] start_kernel+0x88/0x7c0
> [ 0.000000]
> [ 0.000000] SoC Type: MediaTek MT7621 ver:1 eco:3
The stack means CONFIG_TRACING=n, is that right?
That would mean
prom_soc_init()
soc_dev_init()
kzalloc() -> kmalloc()
kmalloc_trace() // after #else /* CONFIG_TRACING */
kmem_cache_alloc(s, flags);
Looks like this path is a small bug in the wasting detection patch, as we
throw away size there.
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, and we should look into the
CONFIG_TRACING=n variant of kmalloc_trace(), to pass orig_size properly.
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