netdev - Re: [PATCH v2 2/2] net: add debugfs files for showing netns refcount tracking info

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Message-ID: <1e717326-8551-419e-b185-5cfb20573b4f@lunn.ch>
Date: Thu, 10 Apr 2025 14:36:26 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Jeff Layton <jlayton@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] net: add debugfs files for showing netns refcount
 tracking info

On Tue, Apr 08, 2025 at 09:36:38AM -0400, Jeff Layton wrote:
> CONFIG_NET_NS_REFCNT_TRACKER currently has no convenient way to display
> its tracking info. Add a new net_ns directory under the debugfs
> ref_tracker directory. Create a directory in there for every netns, with
> refcnt and notrefcnt files that show the currently tracked active and
> passive references.

I think most if not all of this should be moved into the tracker
sources, there is very little which is netdev specific. 

> 
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>  net/core/net_namespace.c | 151 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 151 insertions(+)
> 
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index 4303f2a4926243e2c0ff0c0387383cd8e0658019..7e9dc487f46d656ee4ae3d6d18d35bb2aba2b176 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -1512,3 +1512,154 @@ const struct proc_ns_operations netns_operations = {
>  	.owner		= netns_owner,
>  };
>  #endif
> +
> +#ifdef CONFIG_DEBUG_FS
> +#ifdef CONFIG_NET_NS_REFCNT_TRACKER
> +
> +#include <linux/debugfs.h>
> +
> +static struct dentry *ns_ref_tracker_dir;
> +static unsigned int ns_debug_net_id;
> +
> +struct ns_debug_net {
> +	struct dentry *netdir;
> +	struct dentry *refcnt;
> +	struct dentry *notrefcnt;
> +};
> +
> +#define MAX_NS_DEBUG_BUFSIZE	(32 * PAGE_SIZE)
> +
> +static int
> +ns_debug_tracker_show(struct seq_file *f, void *v)
> +{
> +	struct ref_tracker_dir *tracker = f->private;
> +	int len, bufsize = PAGE_SIZE;
> +	char *buf;
> +
> +	for (;;) {
> +		buf = kvmalloc(bufsize, GFP_KERNEL);
> +		if (!buf)
> +			return -ENOMEM;
> +
> +		len = ref_tracker_dir_snprint(tracker, buf, bufsize);
> +		if (len < bufsize)
> +			break;
> +
> +		kvfree(buf);
> +		bufsize *= 2;
> +		if (bufsize > MAX_NS_DEBUG_BUFSIZE)
> +			return -ENOBUFS;

Maybe consider storing bufsize between calls to dump the tracker? I
guess you then have about the correct size for most calls, and from
looking at len, you can decide to downsize it if needed.

> +static int
> +ns_debug_init_net(struct net *net)
> +{
> +	struct ns_debug_net *dnet = net_generic(net, ns_debug_net_id);
> +	char name[11]; /* 10 decimal digits + NULL term */
> +	int len;
> +
> +	len = snprintf(name, sizeof(name), "%u", net->ns.inum);
> +	if (len >= sizeof(name))
> +		return -EOVERFLOW;
> +
> +	dnet->netdir = debugfs_create_dir(name, ns_ref_tracker_dir);
> +	if (IS_ERR(dnet->netdir))
> +		return PTR_ERR(dnet->netdir);

As i pointed out before, the tracker already has a name. Is that name
useless? Not specific enough? Rather than having two names, maybe
change the name to make it useful. Once it has a usable name, you
should be able to push more code into the core.

       Andrew