linux-kernel - Re: [PATCH v2 4/7] tracefs: dentry lookup crapectomy

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Date: Wed, 31 Jan 2024 23:18:00 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, Linus Torvalds
 <torvalds@...ux-foundation.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Christian Brauner <brauner@...nel.org>,
 Ajay Kaher <ajay.kaher@...adcom.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, stable@...r.kernel.org
Subject: Re: [PATCH v2 4/7] tracefs: dentry lookup crapectomy

On Wed, 31 Jan 2024 22:21:27 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> We (Linus and I) got it wrong. It originally had:
> 
> 	d_add(dentry, NULL);
> 	[..]
> 	return NULL;

OK, so I changed that function to this:

static struct dentry *eventfs_root_lookup(struct inode *dir,
					  struct dentry *dentry,
					  unsigned int flags)
{
	struct eventfs_inode *ei_child;
	struct tracefs_inode *ti;
	struct eventfs_inode *ei;
	const char *name = dentry->d_name.name;

	ti = get_tracefs(dir);
	if (!(ti->flags & TRACEFS_EVENT_INODE))
		return ERR_PTR(-EIO);

	mutex_lock(&eventfs_mutex);

	ei = ti->private;
	if (!ei || ei->is_freed)
		goto out;

	list_for_each_entry(ei_child, &ei->children, list) {
		if (strcmp(ei_child->name, name) != 0)
			continue;
		if (ei_child->is_freed)
			goto out;
		lookup_dir_entry(dentry, ei, ei_child);
		goto out;
	}

	for (int i = 0; i < ei->nr_entries; i++) {
		void *data;
		umode_t mode;
		const struct file_operations *fops;
		const struct eventfs_entry *entry = &ei->entries[i];

		if (strcmp(name, entry->name) != 0)
			continue;

		data = ei->data;
		if (entry->callback(name, &mode, &data, &fops) <= 0)
			goto out;

		lookup_file_dentry(dentry, ei, i, mode, data, fops);
		goto out;
	}
 out:
	mutex_unlock(&eventfs_mutex);
	return NULL;
}

And it passes the make kprobe test. I'll send out a v3 of this patch, and
remove the inc_nlink(dentry->d_parent->d_inode) and the fsnotify as
separate patches as that code was there before Linus touched it.

Thanks,

-- Steve