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Sun, 14 Aug 2022 18:11:45 -0700 (PDT) Date: Sun, 14 Aug 2022 18:11:44 -0700 (PDT) From: David Rientjes To: Waiman Long cc: Christoph Lameter , Pekka Enberg , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Roman Gushchin , 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 In-Reply-To: <20220812183033.346425-1-longman@redhat.com> Message-ID: References: <20220812183033.346425-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660525907; a=rsa-sha256; cv=none; b=2gAnW81tjKLPevjwVkYdDvNi9f53I0hgVYw0iVSlSSxSf3GGWRuQeiRQO0eA6frTuW/cPs KeiES8H0G2bBdOlPqjH0q2JMLBSU3a6jdNxysUDThHeYreKrsR33jH/tfKEXxyKN5JJZQi MeV7P/qNgnsxKfjylWmPVSTiJ/SYTHc= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=OYn6Uq00; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf01.hostedemail.com: domain of rientjes@google.com designates 209.85.216.54 as permitted sender) smtp.mailfrom=rientjes@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660525907; 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=Ne4JOdW2yUxs9Z+rnlNsmRDLyCc2jQEMfG4sisZnaNQ=; b=gtKMaidHuKgOyJNTkG6tOAz6rTBE9HJteLReEmGxkKCTEpGyQJhLqdRsUkIsWMWV2z3OEx hb+LTdNwZjDbdJmSnmCQzXJdZzs6rdnlwMMiHggjkqsEX+LC6llcWshTMXiNtbaIGIgXcZ gaTeIaqzq3+AWchyyFpc0TiacL8i+58= X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 6F9D84004C Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=OYn6Uq00; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf01.hostedemail.com: domain of rientjes@google.com designates 209.85.216.54 as permitted sender) smtp.mailfrom=rientjes@google.com X-Rspam-User: X-Stat-Signature: gnhqhitgibecx71fsqezn9j9yti4fh4q X-HE-Tag: 1660525907-667398 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, 12 Aug 2022, 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 Acked-by: David Rientjes