Re: [PATCH iproute2] ip/netns: avoid redundant mounts

[David Ahern <dsahern@kernel.org>]

On 2/9/26 9:11 PM, Chen Linxuan via B4 Relay wrote:
> From: Chen Linxuan <me@black-desk.cn>
> 
> On Ubuntu 24.04, I observed redundant mounts after adding a netns with
> the commands below:
> 
> 	sudo ip netns add xxx
> 	cat /proc/self/mountinfo | grep /run
> 
> Output:
> 
> 	29 31 0:26 / /run rw,nosuid,nodev,noexec,relatime shared:5 - tmpfs tmpfs ...
> 	...
> 	203 29 0:26 /netns /run/netns rw,nosuid,nodev,noexec,relatime shared:5 - tmpfs tmpfs ...
> 	6443 203 0:4 net:[4026533578] /run/netns/xxx rw shared:917 - nsfs nsfs rw
> 	6444 29 0:4 net:[4026533578] /run/netns/xxx rw shared:917 - nsfs nsfs rw

with this patch I am still seeing 2 entries:

$ sudo ./ip netns add blah
$ cat /proc/self/mountinfo  | grep blah
337 92 0:4 net:[4026532418] /run/netns/blah rw shared:344 - nsfs nsfs rw
338 28 0:4 net:[4026532418] /run/netns/blah rw shared:344 - nsfs nsfs rw

...

> diff --git a/ip/ipnetns.c b/ip/ipnetns.c
> index a20cd8bc7cb8..3a33a3adacee 100644
> --- a/ip/ipnetns.c
> +++ b/ip/ipnetns.c
> @@ -846,6 +846,20 @@ static int netns_add(int argc, char **argv, bool create)
>  			}
>  			return -1;
>  		}
> +
> +		/* Reconfigure NETNS_RUN_DIR to MS_PRIVATE recursively and later
> +		 * MS_SAHRED again to make sure it is placed in a new peer group
> +		 */
> +		if (mount(NETNS_RUN_DIR, NETNS_RUN_DIR, "none", MS_PRIVATE | MS_REC, NULL)) {

line is rather long. please limit line length to about 80 columns except
for print strings like the next line.

> +			fprintf(stderr, "mount --make-private %s failed: %s\n",
> +				NETNS_RUN_DIR, strerror(errno));
> +			if (lock != -1) {
> +				flock(lock, LOCK_UN);
> +				close(lock);
> +			}
> +			return -1;
> +		}
> +
>  		made_netns_run_dir_mount = 1;
>  	}
>  	if (lock != -1) {
> 
> ---
> base-commit: 72f679c0d07629fe9e462c2c52bbe48aaeaa7f83
> change-id: 20260210-netns-redundant-mount-aa2db50eac7d
> 
> Best regards,