Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:4 as permitted sender) client-ip=2620:137:e000::3:4;
Date:   Fri, 27 Oct 2023 12:00:47 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     David Howells <dhowells@redhat.com>,
        Marc Dionne <marc.dionne@auristor.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     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: <20231027100047.GA30884@redhat.com>
References: <20231027095842.GA30868@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20231027095842.GA30868@redhat.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Precedence: bulk

On 10/27, Oleg Nesterov wrote:
>
> read_seqbegin_or_lock() makes no sense unless you make "seq" odd
> after the lockless access failed. See thread_group_cputime() as
> an example, note that it does nextseq = 1 for the 2nd round.

See also

	[PATCH 1/2] seqlock: fix the wrong read_seqbegin_or_lock/need_seqretry documentation
	https://lore.kernel.org/all/20231024120808.GA15382@redhat.com/

> So this code can use read_seqbegin() without changing the current
> behaviour.

I am trying to remove the misuse of read_seqbegin_or_lock(),
then I am going to turn need_seqretry() into

	static inline int need_seqretry(seqlock_t *lock, int *seq)
	{
		int ret = !(*seq & 1) && read_seqretry(lock, *seq);

		if (ret)
			*seq = 1; /* make this counter odd */

		return ret;
	}

Oleg.