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Mon, 03 Oct 2022 00:02:51 -0700 (PDT) Date: Mon, 3 Oct 2022 16:02:46 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Rasmus Villemoes Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add() Message-ID: References: <20220930084742.771804-1-linux@rasmusvillemoes.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220930084742.771804-1-linux@rasmusvillemoes.dk> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664780573; a=rsa-sha256; cv=none; b=HY7WC+kMN6R5ItXWTSaDCcf9NHoqvMmQOkWl0AgJjpd5s8aSdnSl1Ue3NP5h1NY+mYGek0 iLPsZ6qdmRuDijHUBE85xkRoUbzm9M8MG1gvH/PczIlC5Z7ypjhEjohpnZJ7nKSN+txhCn x4ph+RSFthl5ZBy6d8qPHedoSiOa3yQ= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=MQfF98n6; 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dmarc=pass (policy=none) header.from=gmail.com X-Stat-Signature: yepws3dw8wihft6fagm3mwc77fcudt35 X-HE-Tag: 1664780573-610956 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Sep 30, 2022 at 10:47:42AM +0200, Rasmus Villemoes wrote: > The function sysfs_slab_add() has two callers: > > One is slab_sysfs_init(), which first initializes slab_kset, and only > when that succeeds sets slab_state to FULL, and then proceeds to call > sysfs_slab_add() for all previously created slabs. > > The other is __kmem_cache_create(), but only after a > > if (slab_state <= UP) > return 0; > > check. > > So in other words, sysfs_slab_add() is never called without > slab_kset (aka the return value of cache_kset()) being non-NULL. > > And this is just as well, because if we ever did take this path and > called kobject_init(&s->kobj), and then later when called again from > slab_sysfs_init() would end up calling kobject_init_and_add(), we > would hit > > if (kobj->state_initialized) { > /* do not error out as sometimes we can recover */ > pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n", > dump_stack(); > } > > in kobject.c. > > Signed-off-by: Rasmus Villemoes > --- > mm/slub.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 4b98dff9be8e..04a7f75a7b1f 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5937,11 +5937,6 @@ static int sysfs_slab_add(struct kmem_cache *s) > struct kset *kset = cache_kset(s); > int unmergeable = slab_unmergeable(s); > > - if (!kset) { > - kobject_init(&s->kobj, &slab_ktype); > - return 0; > - } > - > if (!unmergeable && disable_higher_order_debug && > (slub_debug & DEBUG_METADATA_FLAGS)) > unmergeable = 1; > -- > 2.37.2 I assumed that it's hit when SLUB failed to initialize slab_kset in slab_sysfs_init(). (Yeah, it is too unlikely, though....) And obviously it's a bug if sysfs_slab_add() is called early than slab_sysfs_init(). -- Thanks, Hyeonggon