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Subject: Re: [PATCH] lockd: don't use timed rebind with TCP
From:   Calum Mackay <calum.mackay@oracle.com>
To:     trondmy@hammerspace.com, anna.schumaker@netapp.com
References: <20201002225750.16452-1-calum.mackay@oracle.com>
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Organization: Oracle
Message-ID: <9f36a510-3721-f454-a2ef-95e5b9beb360@oracle.com>
Date:   Sat, 3 Oct 2020 18:21:12 +0100
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From: Calum Mackay <calum.mackay@oracle.com>
To: trondmy@hammerspace.com, anna.schumaker@netapp.com
Cc: linux-nfs@vger.kernel.org
Message-ID: <9f36a510-3721-f454-a2ef-95e5b9beb360@oracle.com>
Subject: Re: [PATCH] lockd: don't use timed rebind with TCP
References: <20201002225750.16452-1-calum.mackay@oracle.com>
In-Reply-To: <20201002225750.16452-1-calum.mackay@oracle.com>

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Please hold off for now on this one; I think I need to adjust the=20
reclaimer a little.

thanks,
calum.

On 02/10/2020 11:57 pm, Calum Mackay wrote:
> It is possible for nlm_bind_host() to clear XPRT_BOUND whilst a connect=
ion
> worker is in the middle of trying to reconnect. When the latter notices=

> that XPRT_BOUND been cleared under it, in xs_tcp_finish_connecting(),
> that results in:
>=20
> 	xs_tcp_setup_socket: connect returned unhandled error -107
>=20
> Worse, it's possible that the two can get into lockstep, resulting in
> the same behaviour repeated indefinitely, with the above error every
> 300 seconds, without ever recovering, and the connection never being
> established. This is most likely to occur when there's a large number
> of NLM client tasks following a server reboot.
>=20
> Since the timed rebind would seem not to be needed for TCP in any case,=

> whilst the existing connection remains, restrict the timed rebinding to=

> UDP only.
>=20
> For TCP, we will still rebind when needed, e.g. on timeout, connection
> error (including closure), and in the reclaimer.
>=20
> Whilst there, refactor some duplicate code.
>=20
> Signed-off-by: Calum Mackay <calum.mackay@oracle.com>
> ---
>   fs/lockd/host.c | 16 +++++++---------
>   1 file changed, 7 insertions(+), 9 deletions(-)
>=20
> diff --git a/fs/lockd/host.c b/fs/lockd/host.c
> index 0afb6d59bad0..6e98c2ed6ffc 100644
> --- a/fs/lockd/host.c
> +++ b/fs/lockd/host.c
> @@ -439,12 +439,7 @@ nlm_bind_host(struct nlm_host *host)
>   	 * RPC rebind is required
>   	 */
>   	if ((clnt =3D host->h_rpcclnt) !=3D NULL) {
> -		if (time_after_eq(jiffies, host->h_nextrebind)) {
> -			rpc_force_rebind(clnt);
> -			host->h_nextrebind =3D jiffies + NLM_HOST_REBIND;
> -			dprintk("lockd: next rebind in %lu jiffies\n",
> -					host->h_nextrebind - jiffies);
> -		}
> +		nlm_rebind_host(host);
>   	} else {
>   		unsigned long increment =3D nlmsvc_timeout;
>   		struct rpc_timeout timeparms =3D {
> @@ -495,15 +490,18 @@ nlm_bind_host(struct nlm_host *host)
>   }
>  =20
>   /*
> - * Force a portmap lookup of the remote lockd port
> + * Force a portmap lookup of the remote lockd port, unless we're using=
 a
> + * TCP connection.
>    */
>   void
>   nlm_rebind_host(struct nlm_host *host)
>   {
> -	dprintk("lockd: rebind host %s\n", host->h_name);
> -	if (host->h_rpcclnt && time_after_eq(jiffies, host->h_nextrebind)) {
> +	if (unlikely(host->h_proto =3D=3D IPPROTO_UDP) && host->h_rpcclnt &&
> +			time_after_eq(jiffies, host->h_nextrebind)) {
>   		rpc_force_rebind(host->h_rpcclnt);
>   		host->h_nextrebind =3D jiffies + NLM_HOST_REBIND;
> +		dprintk("lockd: rebind host %s; next rebind in %lu jiffies\n",
> +			host->h_name, host->h_nextrebind - jiffies);
>   	}
>   }
>  =20
>=20

--=20
Calum Mackay
Linux Kernel Engineering
Oracle Linux and Virtualisation

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