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From:   "NeilBrown" <neilb@suse.de>
To:     "Chuck Lever" <cel@kernel.org>
Cc:     linux-nfs@vger.kernel.org, "Chuck Lever" <chuck.lever@oracle.com>,
        lorenzo@kernel.org, jlayton@redhat.com, david@fromorbit.com
Subject: Re: [PATCH v2 7/9] SUNRPC: Don't disable BH's when taking sp_lock
In-reply-to: <168842929557.139194.4420161035549339648.stgit@manet.1015granger.net>
References: <168842897573.139194.15893960758088950748.stgit@manet.1015granger.net>,
 <168842929557.139194.4420161035549339648.stgit@manet.1015granger.net>
Date:   Tue, 04 Jul 2023 10:56:08 +1000
Message-id: <168843216897.8939.13310930289540832368@noble.neil.brown.name>
Precedence: bulk

On Tue, 04 Jul 2023, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
>=20
> Consumers of sp_lock now all run in process context. We can avoid
> the overhead of disabling bottom halves when taking this lock.

"now" suggests that something has recently changed so that sp_lock isn't
taken in bh context.  What was that change - I don't see it.

I think svc_data_ready() is called in bh, and that calls
svc_xprt_enqueue() which take sp_lock to add the xprt to ->sp_sockets.=20

Is that not still the case?

NeilBrown


>=20
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/svc_xprt.c |   14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>=20
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index ecbccf0d89b9..8ced7591ce07 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -472,9 +472,9 @@ void svc_xprt_enqueue(struct svc_xprt *xprt)
>  	pool =3D svc_pool_for_cpu(xprt->xpt_server);
> =20
>  	percpu_counter_inc(&pool->sp_sockets_queued);
> -	spin_lock_bh(&pool->sp_lock);
> +	spin_lock(&pool->sp_lock);
>  	list_add_tail(&xprt->xpt_ready, &pool->sp_sockets);
> -	spin_unlock_bh(&pool->sp_lock);
> +	spin_unlock(&pool->sp_lock);
> =20
>  	rqstp =3D svc_pool_wake_idle_thread(xprt->xpt_server, pool);
>  	if (!rqstp) {
> @@ -496,14 +496,14 @@ static struct svc_xprt *svc_xprt_dequeue(struct svc_p=
ool *pool)
>  	if (list_empty(&pool->sp_sockets))
>  		goto out;
> =20
> -	spin_lock_bh(&pool->sp_lock);
> +	spin_lock(&pool->sp_lock);
>  	if (likely(!list_empty(&pool->sp_sockets))) {
>  		xprt =3D list_first_entry(&pool->sp_sockets,
>  					struct svc_xprt, xpt_ready);
>  		list_del_init(&xprt->xpt_ready);
>  		svc_xprt_get(xprt);
>  	}
> -	spin_unlock_bh(&pool->sp_lock);
> +	spin_unlock(&pool->sp_lock);
>  out:
>  	return xprt;
>  }
> @@ -1116,15 +1116,15 @@ static struct svc_xprt *svc_dequeue_net(struct svc_=
serv *serv, struct net *net)
>  	for (i =3D 0; i < serv->sv_nrpools; i++) {
>  		pool =3D &serv->sv_pools[i];
> =20
> -		spin_lock_bh(&pool->sp_lock);
> +		spin_lock(&pool->sp_lock);
>  		list_for_each_entry_safe(xprt, tmp, &pool->sp_sockets, xpt_ready) {
>  			if (xprt->xpt_net !=3D net)
>  				continue;
>  			list_del_init(&xprt->xpt_ready);
> -			spin_unlock_bh(&pool->sp_lock);
> +			spin_unlock(&pool->sp_lock);
>  			return xprt;
>  		}
> -		spin_unlock_bh(&pool->sp_lock);
> +		spin_unlock(&pool->sp_lock);
>  	}
>  	return NULL;
>  }
>=20
>=20
>=20