linux-kernel - Re: [PATCH 0/5] SLUB debugfs improvements based on stackdepot

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Date:   Mon, 28 Feb 2022 20:10:18 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Oliver Glitta <glittao@...il.com>,
        Faiyaz Mohammed <faiyazm@...eaurora.org>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>,
        Marco Elver <elver@...gle.com>,
        Karolina Drobnik <karolinadrobnik@...il.com>,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCH 0/5] SLUB debugfs improvements based on stackdepot

On 2/26/22 08:19, Hyeonggon Yoo wrote:
> On Fri, Feb 25, 2022 at 07:03:13PM +0100, Vlastimil Babka wrote:
>> Hi,
>> 
>> this series combines and revives patches from Oliver's last year
>> bachelor thesis (where I was the advisor) that make SLUB's debugfs
>> files alloc_traces and free_traces more useful.
>> The resubmission was blocked on stackdepot changes that are now merged,
>> as explained in patch 2.
>> 
> 
> Hello. I just started review/testing this series.
> 
> it crashed on my system (arm64)

Hmm, interesting. On x86_64 this works for me and stackdepot is allocated
from memblock. arm64 must have memblock freeing happen earlier or something.
(CCing memblock experts)

> I ran with boot parameter slub_debug=U, and without KASAN.
> So CONFIG_STACKDEPOT_ALWAYS_INIT=n.
> 
> void * __init memblock_alloc_try_nid(
>                         phys_addr_t size, phys_addr_t align,
>                         phys_addr_t min_addr, phys_addr_t max_addr,
>                         int nid)
> {
>         void *ptr;
> 
>         memblock_dbg("%s: %llu bytes align=0x%llx nid=%d from=%pa max_addr=%pa %pS\n",
>                      __func__, (u64)size, (u64)align, nid, &min_addr,
>                      &max_addr, (void *)_RET_IP_);
>         ptr = memblock_alloc_internal(size, align,
>                                            min_addr, max_addr, nid, false);
>         if (ptr)
>                 memset(ptr, 0, size); <--- Crash Here
> 
>         return ptr;
> }
> 
> It crashed during create_boot_cache() -> stack_depot_init() ->
> memblock_alloc().
> 
> I think That's because, in kmem_cache_init(), both slab and memblock is not
> available. (AFAIU memblock is not available after mem_init() because of
> memblock_free_all(), right?)

Hm yes I see, even in x86_64 version mem_init() calls memblock_free_all().
But then, I would expect stack_depot_init() to detect that memblock_alloc()
returns NULL, we print ""Stack Depot hash table allocation failed,
disabling" and disable it. Instead it seems memblock_alloc() returns
something that's already potentially used by somebody else? Sounds like a bug?

> Thanks!
> 
> /*
>  * Set up kernel memory allocators
>  */
> static void __init mm_init(void)
> {
>         /*
>          * page_ext requires contiguous pages,
>          * bigger than MAX_ORDER unless SPARSEMEM.
>          */
>         page_ext_init_flatmem();
>         init_mem_debugging_and_hardening();
>         kfence_alloc_pool();
>         report_meminit();
>         stack_depot_early_init();
>         mem_init();
>         mem_init_print_info();
>         kmem_cache_init();
>         /*
>          * page_owner must be initialized after buddy is ready, and also after
>          * slab is ready so that stack_depot_init() works properly
>          */)
> 
>> Patch 1 is a new preparatory cleanup.
>> 
>> Patch 2 originally submitted here [1], was merged to mainline but
>> reverted for stackdepot related issues as explained in the patch.
>> 
>> Patches 3-5 originally submitted as RFC here [2]. In this submission I
>> have omitted the new file 'all_objects' (patch 3/3 in [2]) as it might
>> be considered too intrusive so I will postpone it for later. The docs
>> patch is adjusted accordingly.
>> 
>> Also available in git, based on v5.17-rc1:
>> https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=slub-stackdepot-v1
>> 
>> I'd like to ask for some review before I add this to the slab tree.
>> 
>> [1] https://lore.kernel.org/all/20210414163434.4376-1-glittao@gmail.com/
>> [2] https://lore.kernel.org/all/20210521121127.24653-1-glittao@gmail.com/
>> 
>> Oliver Glitta (4):
>>   mm/slub: use stackdepot to save stack trace in objects
>>   mm/slub: aggregate and print stack traces in debugfs files
>>   mm/slub: sort debugfs output by frequency of stack traces
>>   slab, documentation: add description of debugfs files for SLUB caches
>> 
>> Vlastimil Babka (1):
>>   mm/slub: move struct track init out of set_track()
>> 
>>  Documentation/vm/slub.rst |  61 +++++++++++++++
>>  init/Kconfig              |   1 +
>>  mm/slub.c                 | 152 +++++++++++++++++++++++++-------------
>>  3 files changed, 162 insertions(+), 52 deletions(-)
>> 
>> -- 
>> 2.35.1
>> 
>> 
>