linux-kernel - Re: [PATCH rcu 14/16] rxrpc: Use call_rcu_hurry() instead of call

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Message-ID: <20230311174607.GA2293352@google.com>
Date:   Sat, 11 Mar 2023 17:46:07 +0000
From:   Joel Fernandes <joel@...lfernandes.org>
To:     David Howells <dhowells@...hat.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rostedt@...dmis.org, Marc Dionne <marc.dionne@...istor.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-afs@...ts.infradead.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH rcu 14/16] rxrpc: Use call_rcu_hurry() instead of
 call_rcu()

On Wed, Nov 30, 2022 at 11:05:22PM +0000, David Howells wrote:
> Joel Fernandes <joel@...lfernandes.org> wrote:
[...] 
> > After your patch, you are still doing a wake up in your call_rcu() callback:
> >
> > - ASSERTCMP(refcount_read(&conn->ref), ==, 0);
> > + if (atomic_dec_and_test(&rxnet->nr_conns))
> > +    wake_up_var(&rxnet->nr_conns);
> > +}
> > 
> > Are you saying the code can now tolerate delays? What if the RCU
> > callback is invoked after arbitrarily long delays making the sleeping
> > process to wait?
> 
> True.  But that now only holds up the destruction of a net namespace and the
> removal of the rxrpc module.

I am guessing not destructing the net namespace soon enough is not an issue.
I do remember (in a different patch) that not tearing down networking things
have a weird side effect to tools that require state to disappear..

> > If you agree, you can convert the call_rcu() to call_rcu_hurry() in
> > your patch itself. Would you be willing to do that? If not, that's
> > totally OK and I can send a patch later once yours is in (after
> > further testing).
> 
> I can add it to part 4 (see my rxrpc-ringless-5 branch) if it is necessary.

I am guessing the conversion to call_rcu_hurry() is still not necessary here,
if it is then consider the conversion.

But yeah feel free to ignore this, I am just pinging here so that it did not
slip through the cracks.

thanks,

 - Joel