linux-kernel - Re: [PATCH v2 3/3] interconnect: Add debugfs test client

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Message-ID: <84f3eae9-fe48-4098-9479-9f4cce216ff0@quicinc.com>
Date:   Tue, 1 Aug 2023 09:59:39 +0530
From:   Pavan Kondeti <quic_pkondeti@...cinc.com>
To:     Mike Tipton <quic_mdtipton@...cinc.com>
CC:     <djakov@...nel.org>, <gregkh@...uxfoundation.org>,
        <rafael@...nel.org>, <corbet@....net>, <linux-pm@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_okukatla@...cinc.com>, <quic_viveka@...cinc.com>,
        <peterz@...radead.org>
Subject: Re: [PATCH v2 3/3] interconnect: Add debugfs test client

On Mon, Jul 31, 2023 at 03:42:47PM -0700, Mike Tipton wrote:
> +static int icc_get_set(void *data, u64 val)
> +{
> +	struct debugfs_path *debugfs_path;
> +	char *src, *dst;
> +	int ret = 0;
> +
> +	mutex_lock(&debugfs_lock);
> +
> +	rcu_read_lock();
> +	src = rcu_dereference(src_node);
> +	dst = rcu_dereference(dst_node);
> +
> +	/*
> +	 * If we've already looked up a path, then use the existing one instead
> +	 * of calling icc_get() again. This allows for updating previous BW
> +	 * votes when "get" is written to multiple times for multiple paths.
> +	 */
> +	cur_path = get_path(src, dst);
> +	if (cur_path) {
> +		rcu_read_unlock();
> +		goto out;
> +	}
> +
> +	src = kstrdup(src, GFP_KERNEL);
> +	dst = kstrdup(dst, GFP_KERNEL);
> +	rcu_read_unlock();
> +

Blocking calls are not allowed from RCU critical section. So we would
need to replace GFP_KERNEL with GFP_ATOMIC.

> +	if (!src || !dst) {
> +		ret = -ENOMEM;
> +		goto err_free;
> +	}
> +
> +	cur_path = icc_get(&pdev->dev, src, dst);
> +	if (IS_ERR(cur_path)) {
> +		ret = PTR_ERR(cur_path);
> +		goto err_free;
> +	}
> +
> +	debugfs_path = kzalloc(sizeof(*debugfs_path), GFP_KERNEL);
> +	if (!debugfs_path) {
> +		ret = -ENOMEM;
> +		goto err_put;
> +	}
> +
> +	debugfs_path->path = cur_path;
> +	debugfs_path->src = src;
> +	debugfs_path->dst = dst;
> +	list_add_tail(&debugfs_path->list, &debugfs_paths);
> +
> +	goto out;
> +
> +err_put:
> +	icc_put(cur_path);
> +err_free:
> +	kfree(src);
> +	kfree(dst);
> +out:
> +	mutex_unlock(&debugfs_lock);
> +	return ret;
> +}