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

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 <[email protected]>
> >> ---
> > 
> > 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.

Leaking size is a problem for custom kernels but not a problem
for distro kernels. Original format can be put under CAP_SYS_ADMIN.

> 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?

I tried to google and grep my local git collection and found nothing.

> >> -	return sysfs_emit(buf, "%pS\n", s->ctor);
> >> +	return sysfs_emit(buf, "%ps\n", s->ctor);