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b=DA+QLZsFO1b3oMEHakbT2Q+8D8aTePXHBYFO/+vHQHQPFBxU0aPqRdGMIW3ih23eZ QT+PU3qEhLCPetMqQp5s3OUHWDUQLFyIJq3X8KRKbQDIgSxP83vYy/a5x1GEYw9/Uo 5IoGIfeBjMBcfXYGm6ypldHoiqyiaN44iiJeOvWRKaNGkz8Ma6PpS4CKY4kK0ZYvY8 +ZxNwgFLxPJbyPTN4gSbHmmlwjqwGDtu49LWEG9ldEEPhK3N97Cl1u06XirgRYt1tH NAg4tt7qin33Y0HrskEoKXQwPbp0akGkHKGllwAnmtmMlF7iCpP3k6JeoCIQ+h2LoP FB5bZAIarXoyw== Message-ID: Date: Tue, 4 Aug 2026 19:25:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] slub: print just the function name in /sys/kernel/slab/*/ctor Content-Language: en-US To: Harry Yoo Cc: Alexey Dobriyan , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org References: <456c0a37-9074-45b5-9be2-a5f2fe345400@p183> <73d28cff-77f5-4cd6-888e-5dce5ebae459@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 024DE1C0011 X-Stat-Signature: p7o1u17945tgzi5cwt4gq47tsxz9rykc X-Rspam-User: X-HE-Tag: 1785864318-166257 X-HE-Meta: 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 VxFI9tzG QAr+eW2z28SSONA7I6jZeiSkE/7sIbRrEFkHTeLr4h4XAsCvu6M8vt3AVrf5rDxDkiIZIRv2q5IkybNpzduQ6E1px/+0vuAxZADDlJsjlq5u+Kn1/ndZYHvmrgAsz8/wFJoq7IekzHYXV563NyK21TsDYWsQ7wpWWu0U0oefRTBjZumaOnR45xvwx72+oH1UwtRbpzHQI3BxFHqdIjGJn5vAYxMJB+EmwKyeuBfU6AXqi2I8pClh74XyZMnRJ7W0ekBhYkzmmV9hBR+mmNkglgzyaLA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? >> 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); >