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

From: John Thomson
Date: Tue Nov 01 2022 - 06:34:20 EST

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@xxxxxxxxxxxxxxxx/
>>
>> 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.
>

With the dump_stack() in place:

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) #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



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) #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] show_stack (/mnt/pool_ssd/code/linux/linux-stable-mt7621/./arch/mips/include/asm/stacktrace.h:43 /mnt/pool_ssd/code/linux/linux-stable-mt7621/arch/mips/kernel/traps.c:223)
[ 0.000000] dump_stack_lvl (/mnt/pool_ssd/code/linux/linux-stable-mt7621/lib/dump_stack.c:107 (discriminator 1))
[ 0.000000] kmem_cache_alloc (/mnt/pool_ssd/code/linux/linux-stable-mt7621/mm/slub.c:3318 /mnt/pool_ssd/code/linux/linux-stable-mt7621/mm/slub.c:3406 /mnt/pool_ssd/code/linux/linux-stable-mt7621/mm/slub.c:3418 /mnt/pool_ssd/code/linux/linux-stable-mt7621/mm/slub.c:3430)
[ 0.000000] prom_soc_init (/mnt/pool_ssd/code/linux/linux-stable-mt7621/arch/mips/ralink/mt7621.c:106 /mnt/pool_ssd/code/linux/linux-stable-mt7621/arch/mips/ralink/mt7621.c:177)
[ 0.000000] prom_init (/mnt/pool_ssd/code/linux/linux-stable-mt7621/arch/mips/ralink/prom.c:64)
[ 0.000000] setup_arch (/mnt/pool_ssd/code/linux/linux-stable-mt7621/arch/mips/kernel/setup.c:786)
[ 0.000000] start_kernel (/mnt/pool_ssd/code/linux/linux-stable-mt7621/init/main.c:279 /mnt/pool_ssd/code/linux/linux-stable-mt7621/init/main.c:477 /mnt/pool_ssd/code/linux/linux-stable-mt7621/init/main.c:960)
[ 0.000000]
[ 0.000000] SoC Type: MediaTek MT7621 ver:1 eco:3


I have not found it yet.


Cheers,
--
John Thomson