Re: [PATCH, mptcp-net] mptcp: fix address removal logic in mptcp_pm_nl_rm_addr

[GangYan <gang.yan@linux.dev>]

On Wed, Nov 05, 2025 at 10:13:56AM +0800, GangYan wrote:
> > On Tue, Nov 04, 2025 at 03:34:38PM +0100, Matthieu Baerts wrote:
> > Hi Gang,
> > 
> > On 04/11/2025 13:34, Gang Yan wrote:
> > > From: Gang Yan <yangang@kylinos.cn>
> > > 
> > > Fix inverted WARN_ON_ONCE condition that prevented normal address
> > > removal counter updates. The current code only executes decrement
> > > logic when the counter is already 0 (abnormal state), while
> > > normal removals (counter > 0) are ignored.
> > 
> > Good catch!
> > 
> > For fixes, we need a Fixes tag:
> > 
> > Fixes: 636113918508 ("mptcp: pm: remove '_nl' from
> > mptcp_pm_nl_rm_addr_received")
> > 
> > Apart from that, it looks good to me:
> > 
> > Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> > 
> > How did you find out about this? I'm surprised out test suite didn't
> > spot it. By chance, do you have a test that can be used to reproduce
> > this issue?
> 
> I've been looking into the work_pending-related issue described in
> #ISSUE 440 and have designed several potentially affected scenarios
Sorry for the wrong number of issue, it should be #ISSUE 549.
> based on mptcp_join tests. Except for the case where endpoints are
> deleted one by one and then re-added via ADD_ADDR (which fails), all
> other related tests have passed. (I'll share some conclusions in the
> corresponding discussion later.)
> 
> By tracing the relevant code, I found that the value of
> 'add_addr_accepted' here does not decrease, which subsequently blocks
> further ADD_ADDR operations. We can verify the value of
> 'add_addr_accepted' in 'delete re-add signal' test, which can be found
> in mptcp_join.sh, using either 'ss' or 'mptcp_diag'. The reason this
> test didn't fail previously is that when the 'add_addr_accepted_limit'
> was set to 3, the test's add_addr operations never reached the limit,
> so no overflow occurred.
> 
> I lean toward using 'ss' to obtain the token and then retrieving the
> 'add_addr_accepted' value via 'mptcp_diag', because when the value is
> zero, ss does not display it. Moreover, using 'mptcp_diag' minimizes
> potential inconsistencies caused by different versions of iproute2,
> making maintenance easier. WDYT?
> 
> Thanks,
> Gang
> > 
> > Cheers,
> > Matt
> > -- 
> > Sponsored by the NGI0 Core fund.
> >