netdev - Re: [PATCH net-next v4 1/2] tcp: Update bind bucket state on port release

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Message-ID: <b22af0eb-e50b-4d5c-a5bc-eb475388da10@redhat.com>
Date: Tue, 16 Sep 2025 12:14:01 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jakub Sitnicki <jakub@...udflare.com>, netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, Neal Cardwell <ncardwell@...gle.com>,
 kernel-team@...udflare.com, Lee Valentine <lvalentine@...udflare.com>
Subject: Re: [PATCH net-next v4 1/2] tcp: Update bind bucket state on port
 release

On 9/13/25 12:09 PM, Jakub Sitnicki wrote:
> Today, once an inet_bind_bucket enters a state where fastreuse >= 0 or
> fastreuseport >= 0 after a socket is explicitly bound to a port, it remains
> in that state until all sockets are removed and the bucket is destroyed.
> 
> In this state, the bucket is skipped during ephemeral port selection in
> connect(). For applications using a reduced ephemeral port
> range (IP_LOCAL_PORT_RANGE socket option), this can cause faster port
> exhaustion since blocked buckets are excluded from reuse.
> 
> The reason the bucket state isn't updated on port release is unclear.
> Possibly a performance trade-off to avoid scanning bucket owners, or just
> an oversight.
> 
> Fix it by recalculating the bucket state when a socket releases a port. To
> limit overhead, each inet_bind2_bucket stores its own (fastreuse,
> fastreuseport) state. On port release, only the relevant port-addr bucket
> is scanned, and the overall state is derived from these.

I'm possibly likely lost, but I think that the bucket state could change
even after inet_bhash2_update_saddr(), but AFAICS it's not updated there.

What am I missing?

Thanks,

Paolo