Re: [dpdk-stable] [dpdk-dev] [PATCH v2] telemetry: fix "in-memory" process socket conflicts

[Kevin Traynor <ktraynor@redhat.com>]

Hi Bruce,

On 24/09/2021 17:18, Bruce Richardson wrote:
> When DPDK is run with --in-memory mode, multiple processes can run
> simultaneously using the same runtime dir. This leads to each process
> removing another process' telemetry socket as it started up, giving
> unexpected behaviour.
> 
> This patch changes that behaviour to first check if the existing socket
> is active. If not, it's an old socket to be cleaned up and can be
> removed. If it is active, telemetry initialization fails and an error
> message is printed out giving instructions on how to remove the error;
> either by using file-prefix to have a different runtime dir (and
> therefore socket path) or by disabling telemetry if it not needed.
> 

telemetry is enabled by default but it may not be used by the 
application. Hitting this issue will cause rte_eal_init() to fail which 
will probably stop or severely limit the application.

So it could change a working application to a non-working one (albeit 
one that doesn't interfere with other process' sockets).

Can it just print a warning that telemetry will not be enabled and 
continue so it's not returning an rte_eal_init failure?

A more minor thing, I see it changes the behaviour from, last one runs 
with telemetry, to, first one runs with telemetry. Though it can be 
figured from the commit message, it might be worth calling that change 
out explicitly.

thanks,
Kevin.

> Fixes: 6dd571fd07c3 ("telemetry: introduce new functionality")
> Cc: stable@dpdk.org
> 
> Reported-by: David Marchand <david.marchand@redhat.com>
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
> v2: fix build error on FreeBSD
> ---
>   lib/telemetry/telemetry.c | 25 ++++++++++++++++++++-----
>   1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/telemetry/telemetry.c b/lib/telemetry/telemetry.c
> index 8304fbf6e9..78508c1a1d 100644
> --- a/lib/telemetry/telemetry.c
> +++ b/lib/telemetry/telemetry.c
> @@ -457,15 +457,30 @@ create_socket(char *path)
>   
>   	struct sockaddr_un sun = {.sun_family = AF_UNIX};
>   	strlcpy(sun.sun_path, path, sizeof(sun.sun_path));
> -	unlink(sun.sun_path);
> +
>   	if (bind(sock, (void *) &sun, sizeof(sun)) < 0) {
>   		struct stat st;
>   
> -		TMTY_LOG(ERR, "Error binding socket: %s\n", strerror(errno));
> -		if (stat(socket_dir, &st) < 0 || !S_ISDIR(st.st_mode))
> +		/* first check if we have a runtime dir */
> +		if (stat(socket_dir, &st) < 0 || !S_ISDIR(st.st_mode)) {
>   			TMTY_LOG(ERR, "Cannot access DPDK runtime directory: %s\n", socket_dir);
> -		sun.sun_path[0] = 0;
> -		goto error;
> +			goto error;
> +		}
> +
> +		/* check if current socket is active */
> +		if (connect(sock, (void *)&sun, sizeof(sun)) == 0) {
> +			TMTY_LOG(ERR, "Error binding telemetry socket, path already in use\n");
> +			TMTY_LOG(ERR, "Use '--file-prefix' to select a different socket path, or '--no-telemetry' to disable\n");
> +			path[0] = 0;
> +			goto error;
> +		}
> +
> +		/* socket is not active, delete and attempt rebind */
> +		unlink(sun.sun_path);
> +		if (bind(sock, (void *) &sun, sizeof(sun)) < 0) {
> +			TMTY_LOG(ERR, "Error binding socket: %s\n", strerror(errno));
> +			goto error;
> +		}
>   	}
>   
>   	if (listen(sock, 1) < 0) {
>