From nobody Sat Apr 11 09:20:55 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ACCD5C00140 for ; Fri, 12 Aug 2022 18:31:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239283AbiHLSbP (ORCPT ); Fri, 12 Aug 2022 14:31:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34568 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230105AbiHLSbM (ORCPT ); Fri, 12 Aug 2022 14:31:12 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E6C2E9C2F2 for ; Fri, 12 Aug 2022 11:31:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1660329069; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=t++bwPtXfG50NpOvD1A/s4vywozAFXDDPLujSLnotyg=; b=ZyJmm+s0wE9umsaMHXCzHyl6CqOs7HkOphP352Bz/mVhs4fwHdN90lrOHNQyaHAXkR6tG8 xgoiA7qwvwc5lvL95/gRx0GwZSHax1qBLMDCG1z3cqlvzGHw4aHqTaq5VyyBejc3UCtv1K ngONLuoSCtk2bxI3z3TeqpCUOFAz0+4= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-193-m9ipcWOaMNqre15G0R9xOg-1; Fri, 12 Aug 2022 14:31:04 -0400 X-MC-Unique: m9ipcWOaMNqre15G0R9xOg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 210B9811E75; Fri, 12 Aug 2022 18:31:02 +0000 (UTC) Received: from llong.com (unknown [10.22.32.88]) by smtp.corp.redhat.com (Postfix) with ESMTP id 95E1F9458A; Fri, 12 Aug 2022 18:31:00 +0000 (UTC) From: Waiman Long To: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Waiman Long Subject: [PATCH v3] mm/slab_common: Deleting kobject in kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock Date: Fri, 12 Aug 2022 14:30:33 -0400 Message-Id: <20220812183033.346425-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" A circular locking problem is reported by lockdep due to the following circular locking dependency. +--> cpu_hotplug_lock --> slab_mutex --> kn->active --+ | | +-----------------------------------------------------+ The forward cpu_hotplug_lock =3D=3D> slab_mutex =3D=3D> kn->active dependen= cy happens in kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); =3D=3D> sysfs_slab_unlink() =3D=3D> kobject_del() =3D=3D> kernfs_remove() =3D=3D> __kernfs_remove() =3D=3D> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); The backward kn->active =3D=3D> cpu_hotplug_lock dependency happens in kernfs_fop_write_iter(): kernfs_get_active(); =3D=3D> slab_attr_store() =3D=3D> cpu_partial_store() =3D=3D> flush_all(): cpus_read_lock() One way to break this circular locking chain is to avoid holding cpu_hotplug_lock and slab_mutex while deleting the kobject in sysfs_slab_unlink() which should be equivalent to doing a write_lock and write_unlock pair of the kn->active virtual lock. Since the kobject structures are not protected by slab_mutex or the cpu_hotplug_lock, we can certainly release those locks before doing the delete operation. Move sysfs_slab_unlink() and sysfs_slab_release() to the newly created kmem_cache_release() and call it outside the slab_mutex & cpu_hotplug_lock critical sections. There will be a slight delay in the deletion of sysfs files if kmem_cache_release() is called indirectly from a work function. Signed-off-by: Waiman Long Acked-by: David Rientjes Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Reviewed-by: Roman Gushchin --- [v3] Move sysfs_slab_unlink() out to kmem_cache_release() and move schedule_work() back right after list_add_tail(). mm/slab_common.c | 45 +++++++++++++++++++++++++++++---------------- 1 file changed, 29 insertions(+), 16 deletions(-) diff --git a/mm/slab_common.c b/mm/slab_common.c index 17996649cfe3..07b948288f84 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -392,6 +392,28 @@ kmem_cache_create(const char *name, unsigned int size,= unsigned int align, } EXPORT_SYMBOL(kmem_cache_create); =20 +#ifdef SLAB_SUPPORTS_SYSFS +/* + * For a given kmem_cache, kmem_cache_destroy() should only be called + * once or there will be a use-after-free problem. The actual deletion + * and release of the kobject does not need slab_mutex or cpu_hotplug_lock + * protection. So they are now done without holding those locks. + * + * Note that there will be a slight delay in the deletion of sysfs files + * if kmem_cache_release() is called indrectly from a work function. + */ +static void kmem_cache_release(struct kmem_cache *s) +{ + sysfs_slab_unlink(s); + sysfs_slab_release(s); +} +#else +static void kmem_cache_release(struct kmem_cache *s) +{ + slab_kmem_cache_release(s); +} +#endif + static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) { LIST_HEAD(to_destroy); @@ -418,11 +440,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct w= ork_struct *work) list_for_each_entry_safe(s, s2, &to_destroy, list) { debugfs_slab_release(s); kfence_shutdown_cache(s); -#ifdef SLAB_SUPPORTS_SYSFS - sysfs_slab_release(s); -#else - slab_kmem_cache_release(s); -#endif + kmem_cache_release(s); } } =20 @@ -437,20 +455,11 @@ static int shutdown_cache(struct kmem_cache *s) list_del(&s->list); =20 if (s->flags & SLAB_TYPESAFE_BY_RCU) { -#ifdef SLAB_SUPPORTS_SYSFS - sysfs_slab_unlink(s); -#endif list_add_tail(&s->list, &slab_caches_to_rcu_destroy); schedule_work(&slab_caches_to_rcu_destroy_work); } else { kfence_shutdown_cache(s); debugfs_slab_release(s); -#ifdef SLAB_SUPPORTS_SYSFS - sysfs_slab_unlink(s); - sysfs_slab_release(s); -#else - slab_kmem_cache_release(s); -#endif } =20 return 0; @@ -465,14 +474,16 @@ void slab_kmem_cache_release(struct kmem_cache *s) =20 void kmem_cache_destroy(struct kmem_cache *s) { + int refcnt; + if (unlikely(!s) || !kasan_check_byte(s)) return; =20 cpus_read_lock(); mutex_lock(&slab_mutex); =20 - s->refcount--; - if (s->refcount) + refcnt =3D --s->refcount; + if (refcnt) goto out_unlock; =20 WARN(shutdown_cache(s), @@ -481,6 +492,8 @@ void kmem_cache_destroy(struct kmem_cache *s) out_unlock: mutex_unlock(&slab_mutex); cpus_read_unlock(); + if (!refcnt && !(s->flags & SLAB_TYPESAFE_BY_RCU)) + kmem_cache_release(s); } EXPORT_SYMBOL(kmem_cache_destroy); =20 --=20 2.31.1