netdev - Re: [PATCH] rxrpc_find_service_conn_rcu: use read_seqbegin() rather than read_seqbegin_or

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Message-ID: <20231101223824.GG32034@redhat.com>
Date: Wed, 1 Nov 2023 23:38:24 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: David Howells <dhowells@...hat.com>
Cc: Marc Dionne <marc.dionne@...istor.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Chuck Lever <chuck.lever@...cle.com>, linux-afs@...ts.infradead.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rxrpc_find_service_conn_rcu: use read_seqbegin() rather
 than read_seqbegin_or_lock()

On 11/01, David Howells wrote:
>
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > Just none of read_seqbegin_or_lock/need_seqretry/done_seqretry
> > helpers make any sense in this code.
>
> I disagree.  I think in at least a couple of cases I do want a locked second
> path

Sorry for confusion. I never said that the 2nd locked pass makes no sense.

My only point is that rxrpc_find_service_conn_rcu() (and more) use
read_seqbegin_or_lock() incorrectly. They can use read_seqbegin() and this
won't change the current behaviour.

So lets change these users first? Then we can discuss the possible changes
in include/linux/seqlock.h and (perhaps) update the users which actually
want the locking on the 2nd pass.

Oleg.