Re: [PATCH] slub: print just the function name in /sys/kernel/slab/*/ctor

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 7/27/26 07:27, Harry Yoo wrote:
> 
> 
> On 7/25/26 10:28 PM, Alexey Dobriyan wrote:
>> Sysfs "ctor" file prints offset/length of the cache's ctor function
>> 
>> 	$ sudo cat /sys/kernel/slab/bdev_cache/ctor
>> 	init_once+0x0/0x10
>> 
>> This is not useful:
>> 
>> Offset will always be 0 because ctor is a function.
>> 
>> I'm not sure what ctor function size is doing here, it should be in
>> /proc/kallsyms
>> 
>> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
>> ---
> 
> I'm not convinced that changing this (without strong justification)
> after exposing it to sysfs for 10+ years is worth the trouble.

Agreed. It's a pity this was exported in the first place. I can't see a
benefit for anyone knowing what the function is called. Should have been at
most a flag whether there's ctor or not.
But possibly a justification is not to leak the function size, which might
be theoretically (although unlikely) a hint to some attack.
Well at least if somebody complains about getting broken, it's trivial to
revert and we can hear about their usecase.
In-tree tools (slabinfo etc) were checked to work properly?

>>  mm/slub.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -9149,7 +9149,7 @@ static ssize_t ctor_show(struct kmem_cache *s, char *buf)
>>  {
>>  	if (!s->ctor)
>>  		return 0;
>> -	return sysfs_emit(buf, "%pS\n", s->ctor);
>> +	return sysfs_emit(buf, "%ps\n", s->ctor);
>>  }
>>  SLAB_ATTR_RO(ctor);
>>  
>