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From: Roman Gushchin To: Waiman Long Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] mm/slab_common: Deleting kobject in kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock Message-ID: References: <20220812183033.346425-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220812183033.346425-1-longman@redhat.com> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660415135; a=rsa-sha256; cv=none; b=7yzyOjNGV9bq2iYzVXtR92RlGmrJJ8dGLrZDwJGy05Ac+jvuwT0JzJP40NBmLGU6o1cBLt CeNqSPMJpYXRUR+ZUUZyWTl7zLWNB4PJM2NJYTpytWJcN3MwssjLJOi5U4MRe24jehsXMd iH74EfUv1BDrm15awJVzpBX7arWOFwY= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=vzG9hIxc; spf=pass (imf20.hostedemail.com: domain of roman.gushchin@linux.dev designates 91.121.223.63 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660415135; h=from:from:sender: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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=XUntDoq6qvPLJTm4y2LJbJzniYTSAJV/ID1PGirdRME=; b=nxvpntZBSZQuNvy+gZc28w26uquzPnrkk1Y9e/VHrUzoOKw0P2ra9PNGfU3cvVJfpgfcl/ ra4wqNx0tJksVNjZz1SxB4w6O+rZxQvsdqi8iV/A0EDPyXTB6t7AeSjkngSd7qXBV/ZMAt cF1JFG73Hqf2qn03/6OKDzJZQpBzbnc= X-Rspam-User: X-Stat-Signature: kb67nzd5poi78ca7drcz8pujfaaecz16 X-Rspamd-Queue-Id: AA7C31C0084 Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=vzG9hIxc; spf=pass (imf20.hostedemail.com: domain of roman.gushchin@linux.dev designates 91.121.223.63 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev; dmarc=pass (policy=none) header.from=linux.dev X-Rspamd-Server: rspam01 X-HE-Tag: 1660415135-255313 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, Aug 12, 2022 at 02:30:33PM -0400, Waiman Long wrote: > 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 ==> slab_mutex ==> kn->active dependency > happens in > > kmem_cache_destroy(): cpus_read_lock(); mutex_lock(&slab_mutex); > ==> sysfs_slab_unlink() > ==> kobject_del() > ==> kernfs_remove() > ==> __kernfs_remove() > ==> kernfs_drain(): rwsem_acquire(&kn->dep_map, ...); > > The backward kn->active ==> cpu_hotplug_lock dependency happens in > > kernfs_fop_write_iter(): kernfs_get_active(); > ==> slab_attr_store() > ==> cpu_partial_store() > ==> 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 Reviewed-by: Roman Gushchin Thank you, Waiman!