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[46.53.134.148]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47febfe5e85sm7167813f8f.14.2026.08.05.02.19.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Aug 2026 02:19:01 -0700 (PDT) Date: Wed, 5 Aug 2026 12:22:42 +0300 From: Alexey Dobriyan To: "Vlastimil Babka (SUSE)" Cc: Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org Subject: Re: [PATCH] slub: print just the function name in /sys/kernel/slab/*/ctor Message-ID: <68e28ff5-8cfd-496a-a895-30de110b0214@p183> References: <456c0a37-9074-45b5-9be2-a5f2fe345400@p183> <73d28cff-77f5-4cd6-888e-5dce5ebae459@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 169CA40008 X-Stat-Signature: uwsejczf4gxt7mgqsg314fuho9fo4gci X-HE-Tag: 1785921542-859590 X-HE-Meta: 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 pDHmKCd1 VmnA8S8r/9b3kVzFWxsE9yXBvWEoZ7yMum4ycRnjLuUc/z0ZI7W+jP7LzOwKLyawy/WkvPgghOqpGYq/j97KLg3JIZAwxKyL1+gEE8SOa1qQWQhFp8fF/7Kgf7RiGEsjXOjJQaNvz8KYqEBu3Oex8J0fLrc21+NcEciMoZf+i+AR1h74iU62tiPBagP0FJAj/Ra9K5UngN6NtL8Ah0055m2Gok4AFl9/jHIOi6ECQhwgwpr2YQhAVVEhPHNmmhARzUua+bVRGeSzj5FW4/aOt73Ue7k9jkMCgc0c5n/815fuZ5PdCQbE6L2jYRzKjtkyQNdQ/YA3JT23dmAsIw2H8+HT3n+/noZlMfNOB4rfm2OW9H38fzZ4gisCnDKte4TgjpmCh/xGTGTVbz3MgJL/KscTyzFh3gIMsBAt0y7lpSnv+FMJ6lv+C5szlG2lFjpnILEo0oRtBuSAqgAM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 > >> >> --- > >> > > >> > 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. My order of preferences is 1) delete +0x0/... part altogeter, 2) when someone complains, restore it as "+0x0/0x4" which is a minimum function size across all archs (or some other fixed fake size). > > >> In-tree tools (slabinfo etc) were checked to work properly? > > > > Looks like it doesn't read ctor at all. > > > > Commit a87615b8f9e2 ("SLUB: slabinfo upgrade") added -o/--ops option > > that should "Display of ctor / dtor etc.", but it reads "ops" attribute > > that has never existed? Bit puzzled. > > Might have been stale code from some previous revisions that included dtor. > > >> >> 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);