netdev - Re: [PATCH net-next v6 1/3] net: tcp/dcpp: prepare for tw

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Message-ID: <20240603121043.4LIAz2Hm@linutronix.de>
Date: Mon, 3 Jun 2024 14:10:43 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Florian Westphal <fw@...len.de>
Cc: Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, mleitner@...hat.com,
	juri.lelli@...hat.com, vschneid@...hat.com, tglozar@...hat.com,
	dsahern@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH net-next v6 1/3] net: tcp/dcpp: prepare for tw_timer
 un-pinning

On 2024-06-03 13:21:52 [+0200], Florian Westphal wrote:
> Theoretically the tw socket can be unlinked from the tw hash already
> (inet_twsk_purge won't encounter it), but timer is still running.
> 
> Only solution I see is to schedule() in tcp_sk_exit_batch() until
> tw_refcount has dropped to the expected value, i.e. something like
> 
> static void tcp_wait_for_tw_timers(struct net *n)
> {
> 	while (refcount_read(&n->ipv4.tcp_death_row.tw_refcount) > 1))
> 		schedule();
> }
> 
> Any better idea?

I need to read the thread but from the context, couldn't you
- grab a refcount
- timer_shutdown_sync() on it
?

Sebastian