Re: [PATCH mptcp-next RFC v4 1/2] mptcp: add MPFailFallback MIB

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly added MIB counter `MPTCP_MIB_MPFAILFALLBACK` is defined and exposed to userspace but never incremented anywhere in the codebase.
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--- Patch [1]: [PATCH mptcp-next RFC v4 1/2] mptcp: add MPFailFallback MIB ---
commit da81a414aec944549813cb91e3dbd055d9e87a03
Author: Chenguang Zhao <zhaochenguang@kylinos.cn>

mptcp: add MPFailFallback MIB

This commit adds a new MIB counter for tracking TCP fallback after accepting
MP_FAIL.

> diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
> index 608cb568897cf..648d4dbca7646 100644
> --- a/net/mptcp/mib.c
> +++ b/net/mptcp/mib.c
[ ... ]
> @@ -88,6 +88,7 @@ static const struct snmp_mib mptcp_snmp_list[] = {
>  	SNMP_MIB_ITEM("MD5SigFallback", MPTCP_MIB_MD5SIGFALLBACK),
>  	SNMP_MIB_ITEM("MD5SigReset", MPTCP_MIB_MD5SIGRESET),
>  	SNMP_MIB_ITEM("DssFallback", MPTCP_MIB_DSSFALLBACK),
> +	SNMP_MIB_ITEM("MPFailFallback", MPTCP_MIB_MPFAILFALLBACK),

[Severity: Medium]
Is this counter actually incremented anywhere in the codebase?

It appears that MPTCP_MIB_MPFAILFALLBACK is defined and exposed here, but it
is never passed to MPTCP_INC_STATS() or used in tracking functions like
mptcp_try_fallback() within this patch.

Without being incremented when a fallback actually occurs, won't this counter
just permanently read zero when queried by userspace?

>  	SNMP_MIB_ITEM("DssReset", MPTCP_MIB_DSSRESET),
>  	SNMP_MIB_ITEM("SimultConnectFallback", MPTCP_MIB_SIMULTCONNFALLBACK),
>  	SNMP_MIB_ITEM("FallbackFailed", MPTCP_MIB_FALLBACKFAILED),

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Sashiko AI review · https://sashiko.dev/#/patchset/20260818091417.2200986-1-chenguang.zhao@linux.dev?part=1