linux-kernel - Re: [PATCH v4] fuse: new work queue to periodically invalidate expired dentries

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Message-ID: <87ldnfmy31.fsf@wotan.olymp>
Date: Tue, 19 Aug 2025 10:59:14 +0100
From: Luis Henriques <luis@...lia.com>
To: Chunsheng Luo <luochunsheng@...c.edu>
Cc: bernd@...ernd.com,  david@...morbit.com,  kernel-dev@...lia.com,
  laura.promberger@...n.ch,  linux-fsdevel@...r.kernel.org,
  linux-kernel@...r.kernel.org,  mharvey@...ptrading.com,
  miklos@...redi.hu
Subject: Re: [PATCH v4] fuse: new work queue to periodically invalidate
 expired dentries

On Tue, Aug 19 2025, Chunsheng Luo wrote:

> On Mon,  7 Jul 2025 16:34:13 Luis Henriques wrote:
>
>>+static void fuse_dentry_tree_add_node(struct dentry *dentry)
>>+{
>>+	struct fuse_conn *fc = get_fuse_conn_super(dentry->d_sb);
>>+	struct fuse_dentry *fd = dentry->d_fsdata;
>>+	struct fuse_dentry *cur;
>>+	struct rb_node **p, *parent = NULL;
>>+	bool start_work = false;
>>+
>>+	if (!fc->inval_wq)
>>+		return;
>
> First check.
>
>>+
>>+	spin_lock(&fc->dentry_tree_lock);
>>+
>>+	if (!fc->inval_wq) {
>>+		spin_unlock(&fc->dentry_tree_lock);
>>+		return;
>>+	}
>
> Check again.
>
> I don't think the if (!fc->inval_wq) check needs to be re-evaluated
> while holding the lock. The reason is that the inval_wq variable 
> doesn't appear to require lock protection. It only gets assigned 
> during fuse_conn_init and fuse_conn_destroy. Furthermore, 
> in fuse_conn_destroy we set inval_wq to zero without holding a lock, 
> and then synchronously cancel any pending work items. 
>
> Therefore, performing this check twice with if (!fc->inval_wq) 
> seems unnecessary.

Thank you for your feedback, Chunsheng.  Having two checks here was just a
small optimisation, the second one is the _real_ one.  So yeah, I guess
it's fine to drop the first one.

Cheers,
-- 
Luís

> Also, in the subject, it would be more appropriate to change
> "work queue" to "workqueue".
>
> Thanks
> Chunsheng Luo
>
>>+
>>+	start_work = RB_EMPTY_ROOT(&fc->dentry_tree);
>>+	__fuse_dentry_tree_del_node(fc, fd);
>>+
>>+	p = &fc->dentry_tree.rb_node;
>>+	while (*p) {
>>+		parent = *p;
>>+		cur = rb_entry(*p, struct fuse_dentry, node);
>>+		if (fd->time > cur->time)
>>+			p = &(*p)->rb_left;
>>+		else
>>+			p = &(*p)->rb_right;
>>+	}
>>+	rb_link_node(&fd->node, parent, p);
>>+	rb_insert_color(&fd->node, &fc->dentry_tree);
>>+	spin_unlock(&fc->dentry_tree_lock);
>>+
>>+	if (start_work)
>>+		schedule_delayed_work(&fc->dentry_tree_work,
>>+				      secs_to_jiffies(fc->inval_wq));
>>+}