Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 23 Jun 2023 14:25:54 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Qi Zheng <zhengqi.arch@bytedance.com>
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,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        intel-gfx@lists.freedesktop.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-nfs@vger.kernel.org, linux-xfs@vger.kernel.org,
        linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 29/29] mm: shrinker: move shrinker-related code into a
 separate file
Message-ID: <20230623052554.GA11471@google.com>
References: <20230622085335.77010-1-zhengqi.arch@bytedance.com>
 <20230622085335.77010-30-zhengqi.arch@bytedance.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230622085335.77010-30-zhengqi.arch@bytedance.com>
Precedence: bulk

On (23/06/22 16:53), Qi Zheng wrote:
> +/*
> + * Remove one
> + */
> +void unregister_shrinker(struct shrinker *shrinker)
> +{
> +	struct dentry *debugfs_entry;
> +	int debugfs_id;
> +
> +	if (!(shrinker->flags & SHRINKER_REGISTERED))
> +		return;
> +
> +	shrinker_put(shrinker);
> +	wait_for_completion(&shrinker->completion_wait);
> +
> +	mutex_lock(&shrinker_mutex);
> +	list_del_rcu(&shrinker->list);

Should this function wait for RCU grace period(s) before it goes
touching shrinker fields?

> +	shrinker->flags &= ~SHRINKER_REGISTERED;
> +	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> +		unregister_memcg_shrinker(shrinker);
> +	debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
> +	mutex_unlock(&shrinker_mutex);
> +
> +	shrinker_debugfs_remove(debugfs_entry, debugfs_id);
> +
> +	kfree(shrinker->nr_deferred);
> +	shrinker->nr_deferred = NULL;
> +}
> +EXPORT_SYMBOL(unregister_shrinker);

[..]

> +void shrinker_free(struct shrinker *shrinker)
> +{
> +	kfree(shrinker);
> +}
> +EXPORT_SYMBOL(shrinker_free);
> +
> +void unregister_and_free_shrinker(struct shrinker *shrinker)
> +{
> +	unregister_shrinker(shrinker);
> +	kfree_rcu(shrinker, rcu);
> +}

Seems like this

	unregister_shrinker();
	shrinker_free();

is not exact equivalent of this

	unregister_and_free_shrinker();