Re: [PATCH mptcp-next RFC v5 1/3] mptcp: add MPFailFallback MIB counter

[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 MPFailFallback is never actually incremented, rendering the feature non-functional.
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--- Patch [1]: [PATCH mptcp-next RFC v5 1/3] mptcp: add MPFailFallback MIB counter ---
commit 1a92bfe5b7b4b89111b623a355d85f37a5901375
Author: Chenguang Zhao <zhaochenguang@kylinos.cn>

mptcp: add MPFailFallback MIB counter
    
Track fallback triggered by MP_FAIL reception.

> diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
> index 608cb568897cf..e1211ad621c9b 100644
> --- a/net/mptcp/mib.c
> +++ b/net/mptcp/mib.c
> @@ -91,6 +91,7 @@ static const struct snmp_mib mptcp_snmp_list[] = {
>  	SNMP_MIB_ITEM("DssReset", MPTCP_MIB_DSSRESET),
>  	SNMP_MIB_ITEM("SimultConnectFallback", MPTCP_MIB_SIMULTCONNFALLBACK),
>  	SNMP_MIB_ITEM("FallbackFailed", MPTCP_MIB_FALLBACKFAILED),
> +	SNMP_MIB_ITEM("MPFailFallback", MPTCP_MIB_MPFAILFALLBACK),
>  	SNMP_MIB_ITEM("WinProbe", MPTCP_MIB_WINPROBE),
>  	SNMP_MIB_ITEM("BacklogDrop", MPTCP_MIB_BACKLOGDROP),
>  	SNMP_MIB_ITEM("RcvPruned", MPTCP_MIB_RCVPRUNED),
> diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
> index 1ebdb55e95343..b006fc8cc848b 100644
> --- a/net/mptcp/mib.h
> +++ b/net/mptcp/mib.h
> @@ -94,6 +94,7 @@ enum linux_mptcp_mib_field {
>  	MPTCP_MIB_DSSRESET,		/* MP_RST: bad data mapping */
>  	MPTCP_MIB_SIMULTCONNFALLBACK,	/* Simultaneous connect */
>  	MPTCP_MIB_FALLBACKFAILED,	/* Can't fallback due to msk status */
> +	MPTCP_MIB_MPFAILFALLBACK,	/* Fallback after MP_FAIL received */

[Severity: Medium]
Is there missing instrumentation for this new counter?

The commit adds the MPTCP_MIB_MPFAILFALLBACK counter to mptcp_snmp_list and
linux_mptcp_mib_field, but there doesn't appear to be any code in this patch
that actually increments it. When an MP_FAIL reception triggers a fallback,
should there be a call to update this counter?

Without an increment, it seems the counter will perpetually remain at 0 and
won't accurately track the fallbacks.

>  	MPTCP_MIB_WINPROBE,		/* MPTCP-level zero window probe */
>  	MPTCP_MIB_BACKLOGDROP,		/* Backlog over memory limit */
>  	MPTCP_MIB_RCVPRUNED,		/* Dropped due to memory constraints */

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260819112112.1985121-1-chenguang.zhao@linux.dev?part=1