From: Vlastimil Babka <vbabka@suse.cz>
To: Feng Tang <feng.tang@intel.com>
Cc: John Thomson <lists@johnthomson.fastmail.com.au>,
Hyeonggon Yoo <42.hyeyoo@gmail.com>,
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" <linux-mips@vger.kernel.org>
Subject: Re: [PATCH v6 1/4] mm/slub: enable debugging memory wasting of kmalloc
Date: Thu, 3 Nov 2022 09:33:28 +0100 [thread overview]
Message-ID: <f88a5d34-de05-25d7-832d-36b3a3eddd72@suse.cz> (raw)
In-Reply-To: <Y2NXiiAF6V2DnBrB@feng-clx>
On 11/3/22 06:54, Feng Tang wrote:
> On Wed, Nov 02, 2022 at 04:22:37PM +0800, Vlastimil Babka wrote:
>> On 11/1/22 11:33, John Thomson wrote:
> [...]
>> >
>> > [ 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) #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?
>
> Yes, from the kconfig, CONFIG_TRACING is not set.
>
>> 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.
>
> Yes, from the code reading and log from John, it is.
>
> One strange thing is, I reset the code to v6.0, and found that
> __kmem_cache_alloc_lru() also access the 's->object_size'
>
> 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);
> ...
> }
>
> And from John's dump_stack() info, this call is also where the NULL pointer
> happens, which I still can't figue out.
>
>> 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.
next prev parent reply other threads:[~2022-11-03 8:33 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-13 6:54 [PATCH v6 0/4] mm/slub: some debug enhancements for kmalloc Feng Tang
2022-09-13 6:54 ` [PATCH v6 1/4] mm/slub: enable debugging memory wasting of kmalloc Feng Tang
2022-09-23 11:43 ` Vlastimil Babka
2022-09-24 7:08 ` Feng Tang
2022-10-30 19:23 ` John Thomson
2022-10-30 21:30 ` Vlastimil Babka
2022-10-31 2:36 ` Feng Tang
2022-10-31 10:05 ` John Thomson
2022-10-31 11:36 ` Hyeonggon Yoo
2022-10-31 11:42 ` Feng Tang
2022-11-01 0:18 ` John Thomson
2022-11-01 2:41 ` John Thomson
2022-11-01 7:57 ` Feng Tang
2022-11-01 9:20 ` John Thomson
2022-11-01 9:31 ` Hyeonggon Yoo
2022-11-01 10:33 ` John Thomson
2022-11-01 10:42 ` Hyeonggon Yoo
2022-11-01 13:55 ` Feng Tang
2022-11-01 19:39 ` John Thomson
2022-11-02 6:08 ` Feng Tang
2022-11-02 7:16 ` Hyeonggon Yoo
2022-11-03 7:18 ` Feng Tang
2022-11-03 7:45 ` John Thomson
2022-11-03 8:16 ` Feng Tang
2022-11-02 8:22 ` Vlastimil Babka
2022-11-03 5:54 ` Feng Tang
2022-11-03 8:33 ` Vlastimil Babka [this message]
2022-11-03 14:16 ` Feng Tang
2022-11-03 14:36 ` Hyeonggon Yoo
2022-11-03 16:57 ` Vlastimil Babka
2022-11-03 17:35 ` Vlastimil Babka
2022-11-04 3:52 ` Feng Tang
2022-09-13 6:54 ` [PATCH v6 2/4] mm/slub: only zero the requested size of buffer for kzalloc Feng Tang
2022-09-26 19:11 ` Andrey Konovalov
2022-09-26 20:15 ` Kees Cook
2022-09-27 1:22 ` Feng Tang
2022-09-27 2:42 ` Feng Tang
2022-10-13 14:00 ` Andrey Konovalov
2022-10-14 5:59 ` Feng Tang
2022-09-13 6:54 ` [PATCH v6 3/4] mm: kasan: Add free_meta size info in struct kasan_cache Feng Tang
2022-09-20 19:20 ` Andrey Konovalov
2022-09-21 12:02 ` Feng Tang
2022-09-24 18:05 ` Andrey Konovalov
2022-09-25 11:26 ` Feng Tang
2022-09-25 16:31 ` Andrey Konovalov
2022-09-27 3:03 ` Feng Tang
2022-09-13 6:54 ` [PATCH v6 4/4] mm/slub: extend redzone check to extra allocated kmalloc space than requested Feng Tang
2022-09-13 8:53 ` Hyeonggon Yoo
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