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

[Harry Yoo <harry@kernel.org>]

On Wed, Aug 05, 2026 at 12:22:42PM +0300, Alexey Dobriyan wrote:
> On Tue, Aug 04, 2026 at 07:25:15PM +0200, Vlastimil Babka (SUSE) wrote:
> > On 8/2/26 07:13, Harry Yoo wrote:
> > > On Thu, Jul 30, 2026 at 04:15:26PM +0200, Vlastimil Babka (SUSE) wrote:
> > >> 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.
> > > 
> > > Agreed.
> > > 
> > >> But possibly a justification is not to leak the function size, which might
> > >> be theoretically (although unlikely) a hint to some attack.
> > > 
> > > ...but you need to be the owner (root) to read this :P 
> > > 
> > >> Well at least if somebody complains about getting broken, it's trivial to
> > >> revert and we can hear about their usecase.
> > > 
> > > If we were to experiment with this, we'll change it to print a flag
> > > rather than the ctor's name, right?
> > 
> > Yep, let's try that. Alexey?
> 
> I don't mind ctor name, it is internal implementation detail,
> but offset/size are kind of useless.

I thought Vlastimil meant ctor name is also useless and suggested
it making it a flag (0/1) to represent whether the cache has a ctor or
not.

Or do you think there's a scenario where ctor name is useful to know? 

-- 
Cheers,
Harry / Hyeonggon