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Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker Content-Language: en-US To: Peter Zijlstra Cc: akpm@linux-foundation.org, david@fromorbit.com, tkhai@ya.ru, vbabka@suse.cz, roman.gushchin@linux.dev, djwong@kernel.org, brauner@kernel.org, paulmck@kernel.org, tytso@mit.edu, steven.price@arm.com, cel@kernel.org, senozhatsky@chromium.org, yujie.liu@intel.com, gregkh@linuxfoundation.org, muchun.song@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, linux-erofs@lists.ozlabs.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-nfs@vger.kernel.org, linux-mtd@lists.infradead.org, rcu@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-bcache@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org References: <20230724094354.90817-1-zhengqi.arch@bytedance.com> <20230724094354.90817-4-zhengqi.arch@bytedance.com> <20230724122549.GA3731903@hirez.programming.kicks-ass.net> From: Qi Zheng In-Reply-To: <20230724122549.GA3731903@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi Peter, On 2023/7/24 20:25, Peter Zijlstra wrote: > On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote: > >> +void shrinker_unregister(struct shrinker *shrinker) >> +{ >> + struct dentry *debugfs_entry; >> + int debugfs_id; >> + >> + if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED)) >> + return; >> + >> + down_write(&shrinker_rwsem); >> + list_del(&shrinker->list); >> + shrinker->flags &= ~SHRINKER_REGISTERED; >> + if (shrinker->flags & SHRINKER_MEMCG_AWARE) >> + unregister_memcg_shrinker(shrinker); >> + debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); >> + up_write(&shrinker_rwsem); >> + >> + shrinker_debugfs_remove(debugfs_entry, debugfs_id); > > Should there not be an rcu_barrier() right about here? The shrinker_debugfs_remove() will wait for debugfs_file_put() to return, so when running here, all shrinker debugfs operations have been completed. And the slab shrink will hold the read lock of shrinker_rwsem to traverse the shrinker_list, so when we hold the write lock of shrinker_rwsem to delete the shrinker from the shrinker_list, the shrinker will not be executed again. So I think there is no need to add a rcu_barrier() here. Please let me know if I missed something. Thanks, Qi > >> + >> + kfree(shrinker->nr_deferred); >> + shrinker->nr_deferred = NULL; >> + >> + kfree(shrinker); >> +} >> +EXPORT_SYMBOL(shrinker_unregister); >