linux-kernel - Re: [PATCH v2] mm, slab: clean up slab->obj

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Message-ID: <6a2b474c-764e-434c-be23-2f366b81c839@suse.cz>
Date: Tue, 22 Apr 2025 09:10:54 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>,
 Zhenhua Huang <quic_zhenhuah@...cinc.com>
Cc: cl@...ux.com, rientjes@...gle.com, roman.gushchin@...ux.dev,
 harry.yoo@...cle.com, pasha.tatashin@...een.com, akpm@...ux-foundation.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, quic_tingweiz@...cinc.com,
 stable@...r.kernel.org
Subject: Re: [PATCH v2] mm, slab: clean up slab->obj_exts always

On 4/21/25 18:02, Suren Baghdasaryan wrote:
> On Mon, Apr 21, 2025 at 12:52 AM Zhenhua Huang
> <quic_zhenhuah@...cinc.com> wrote:
>>
>> When memory allocation profiling is disabled at runtime or due to an
>> error, shutdown_mem_profiling() is called: slab->obj_exts which
>> previously allocated remains.
>> It won't be cleared by unaccount_slab() because of
>> mem_alloc_profiling_enabled() not true. It's incorrect, slab->obj_exts
>> should always be cleaned up in unaccount_slab() to avoid following error:
>>
>> [...]BUG: Bad page state in process...
>> ..
>> [...]page dumped because: page still charged to cgroup
>>
>> Cc: stable@...r.kernel.org
>> Fixes: 21c690a349ba ("mm: introduce slabobj_ext to support slab object extensions")
>> Signed-off-by: Zhenhua Huang <quic_zhenhuah@...cinc.com>
>> Acked-by: David Rientjes <rientjes@...gle.com>
>> Acked-by: Harry Yoo <harry.yoo@...cle.com>
>> Tested-by: Harry Yoo <harry.yoo@...cle.com>
> 
> Acked-by: Suren Baghdasaryan <surenb@...gle.com>
> 
>> ---
>>  mm/slub.c | 12 ++++++++----
>>  1 file changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 566eb8b8282d..a98ce1426076 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -2028,8 +2028,8 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
>>         return 0;
>>  }
>>
>> -/* Should be called only if mem_alloc_profiling_enabled() */
>> -static noinline void free_slab_obj_exts(struct slab *slab)
>> +/* Free only if slab_obj_exts(slab) */
> 
> nit: the above comment is unnecessary. It's quite obvious from the code.

Agreed, I've removed it locally and added the patch to slab/for-next-fixes
Thanks!

>> +static inline void free_slab_obj_exts(struct slab *slab)
>>  {
>>         struct slabobj_ext *obj_exts;
>>
>> @@ -2601,8 +2601,12 @@ static __always_inline void account_slab(struct slab *slab, int order,
>>  static __always_inline void unaccount_slab(struct slab *slab, int order,
>>                                            struct kmem_cache *s)
>>  {
>> -       if (memcg_kmem_online() || need_slab_obj_ext())
>> -               free_slab_obj_exts(slab);
>> +       /*
>> +        * The slab object extensions should now be freed regardless of
>> +        * whether mem_alloc_profiling_enabled() or not because profiling
>> +        * might have been disabled after slab->obj_exts got allocated.
>> +        */
>> +       free_slab_obj_exts(slab);
>>
>>         mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
>>                             -(PAGE_SIZE << order));
>> --
>> 2.34.1
>>