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Date:   Wed, 1 Nov 2023 23:38:24 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     David Howells <dhowells@redhat.com>
Cc:     Marc Dionne <marc.dionne@auristor.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Chuck Lever <chuck.lever@oracle.com>,
        linux-afs@lists.infradead.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rxrpc_find_service_conn_rcu: use read_seqbegin() rather
 than read_seqbegin_or_lock()
Message-ID: <20231101223824.GG32034@redhat.com>
References: <20231101204023.GC32034@redhat.com>
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 <1952182.1698853516@warthog.procyon.org.uk>
 <20231101202302.GB32034@redhat.com>
 <1959105.1698873750@warthog.procyon.org.uk>
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On 11/01, David Howells wrote:
>
> Oleg Nesterov <oleg@redhat.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.